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This book provides reviews and primary research articles that discuss the replication, repair, maintenance, and structures of plant organelle genomes. Rearrangements of these genomes are common and provide a way to distinguish closely related plant species. Some articles in the book discuss recent advances in identifying specific proteins and potential mechanisms involved in DNA replication, recombination, and repair in plant mitochondria and chloroplasts.

The use of unmanned aerial vehicles (UAVs) plays an important role in supporting human activities. Man is concentrating more and more on intellectual work, and trying to automate practical activities as much as possible in order to increase their efficiency. In this regard, the use of drones is increasingly becoming a key aspect of this automation process, offering many advantages, including agility, efficiency and reduced risk, especially in dangerous missions. Hence, this Special Issue focuses on applications, platforms and services where UAVs can be used as facilitators for the task at hand, also keeping in mind that security should be addressed from its different perspectives, ranking from communications security to operational security, and furthermore considering privacy issues.

Antimicrobial resistance (AMR) is a global problem with extremely complex epidemiology involving the direct and indirect transmission of antibiotic resistant pathogens and mobile genetic elements between humans, animals, and the environment. AMR is, therefore, recognized as a ''One Health'' issue. Data that describe AMR prevalence and trends are required to enable the judicious and prudent use of antimicrobials in animals, which has implications both from veterinary and animal welfare aspects as well as from a zoonotic and public health perspective. Horses are a potential reservoir of AMR for humans due to close human-animal contact, as was demonstrated with shared human and horse methicillin-resistant Staphylococcus aureus (MRSA) strains causing outbreaks in equine hospitals. Extended-spectrum beta-lactamase-producing Enterobacteriaceae, considered as clinically and economically important to the AMR burden in human and veterinary medicine, has been reported in both community and clinic equine populations. Strains of Enterobacteriaceae pose a major worldwide threat due to the geographical expansion of ESBL-producing clones as well as the horizontal interspecies dissemination of ESBL-encoding plasmids and genes. In human medicine, ESBL-E infection is associated with increased morbidity, mortality, length of hospital stay, delay of targeted appropriate treatment, and higher costs. These issues also need to be addressed in horses. This Special Issue on AMR in horses encompasses several papers that describe the prevalence, risk factors, and molecular data on MDR bacteria in healthy horses in Canada, Japan, Spain, and Israel, in addition to papers that describe the clinical impact of MDR bacteria in diseased horses in Austria, USA, France and Israel.

"Smart Sensing Technologies for Agriculture" is a Special Issue of Sensors that includes 14 research papers on diverse topics about the measurement of physical, chemical, and biological characteristics of soil, plants, and animals related to modern farming practices.

This issue brings together a collection of papers that provide economic insights into the modern energy market, which is still dominated by crude oil but has expanded to incorporate new energy sources in the form of coal, natural gas, and a mixture of renewable energy sources. Given the differences in the dynamics at play with different energy sources, particularly in relation to price determination, the impact they have on the environment, their importance in the energy mix and energy policy, and so forth, it has become imperative to check their behavior using economic models. Papers 1-3 provide some perspective on oil price determination by focusing on the time-varying nature of supply shocks linked to oil producers (Paper 1), OPEC''s announcements (2), and the heterogeneous interconnections of supply or demand shocks over time horizons and different countries (3). Papers 4-6 compare different energy sources within the energy market and other markets (4); explore the importance of energy storage in the electricity market (5); and examine the dynamic relationship between prices of substitutes (oil price) on the natural gas market in China (6). The final four studies examine the impact of renewable and nonrenewable energy on the macroeconomy and the environment.

The paradigm in the design of all human activity that requires energy for its development must change from the past. We must change the processes of product manufacturing and functional services. This is necessary in order to mitigate the ecological footprint of man on the Earth, which cannot be considered as a resource with infinite capacities. To do this, every single process must be analyzed and modified, with the aim of decarbonising each production sector. This collection of articles has been assembled to provide ideas and new broad-spectrum contributions for these purposes.

In recent years, the advances and abilities of computer software have substantially increased the number of scientific publications that seek to introduce new probabilistic modelling frameworks, including continuous and discrete approaches, and univariate and multivariate models. Many of these theoretical and applied statistical works are related to distributions that try to break the symmetry of the normal distribution and other similar symmetric models, mainly using Azzalini''s scheme. This strategy uses a symmetric distribution as a baseline case, then an extra parameter is added to the parent model to control the skewness of the new family of probability distributions. The most widespread and popular model is the one based on the normal distribution that produces the skewed normal distribution. In this Special Issue on symmetric and asymmetric distributions, works related to this topic are presented, as well as theoretical and applied proposals that have connections with and implications for this topic. Immediate applications of this line of work include different scenarios such as economics, environmental sciences, biometrics, engineering, health, etc. This Special Issue comprises nine works that follow this methodology derived using a simple process while retaining the rigor that the subject deserves. Readers of this Issue will surely find future lines of work that will enable them to achieve fruitful research results.

In recent years, various families of fractional-order integral and derivative operators, such as those named after Riemann-Liouville, Weyl, Hadamard, Grunwald-Letnikov, Riesz, Erdelyi-Kober, Liouville-Caputo, and so on, have been found to be remarkably important and fruitful, due mainly to their demonstrated applications in numerous seemingly diverse and widespread areas of the mathematical, physical, chemical, engineering, and statistical sciences. Many of these fractional-order operators provide interesting, potentially useful tools for solving ordinary and partial differential equations, as well as integral, differintegral, and integro-differential equations; fractional-calculus analogues and extensions of each of these equations; and various other problems involving special functions of mathematical physics and applied mathematics, as well as their extensions and generalizations in one or more variables. For this Special Issue, we invite and welcome review, expository, and original research articles dealing with the recent advances in the theory of fractional-order integral and derivative operators and their multidisciplinary applications.

Arterial hypertension affects about 1 billion people worldwide and it is the strongest modifiable risk factor for cardiovascular disease and related disability. Since the initial discovery of rare monogenic disorders with large effects, the role of genomics has evolved into large genome-wide association studies detecting common variants with a modest effect size. Similarly, pharmacogenomics has emerged as a new tool for understanding variability in drug response, to maximize efficacy and reduce toxicity. This book presents the most recent advances in the field of genetics and genomics of arterial hypertension and their potential impact on clinical management. The book is a useful tool for clinicians but also to the research community and those who want to be updated in the field.

The paradigm in the design of all human activity that requires energy for its development must change from the past. We must change the processes of product manufacturing and functional services. This is necessary in order to mitigate the ecological footprint of man on the Earth, which cannot be considered as a resource with infinite capacities. To do this, every single process must be analyzed and modified, with the aim of decarbonising each production sector. This collection of articles has been assembled to provide ideas and new broad-spectrum contributions for these purposes.

This Special Issue includes manuscripts about soil erosion and degradation processes and the accelerated rates due to hydrological processes and climate change. The new research included in this issue focuses on measurements, modeling, and experiments in field or laboratory conditions developed at different scales (pedon, hillslope, and catchment). This Special Issue received investigations from different parts of the world such as Ethiopia, Morocco, China, Iran, Italy, Portugal, Greece, and Spain, among others. We are happy to see that all papers presented findings characterized as unconventional, provocative, innovative, and methodologically new. We hope that the readers of the journal Water can enjoy and learn about hydrology and soil erosion using the published material, and share the results with the scientific community, policymakers, and stakeholders to continue this amazing adventure, facing plenty of issues and challenges.

In recent years, the industrial environment has been changing radically due to the introduction of concepts and technologies based on the fourth industrial revolution, also known as Industry 4.0. After the introduction of Industry 4.0 in large enterprises, SMEs have moved into the focus, as they are the backbone of many economies. Small organizations are increasingly proactive in improving their operational processes, which is a good starting point for introducing the new concepts of Industry 4.0. The readiness of SME-adapted Industry 4.0 concepts and the organizational capability of SMEs to meet this challenge exist only in some areas. This reveals the need for further research and action plans for preparing SMEs in a technical and organizational direction. Therefore, special research and investigations are needed for the implementation of Industry 4.0 technologies and concepts in SMEs. SMEs will only achieve Industry 4.0 by following SME-customized implementation strategies and approaches and realizing SME-adapted concepts and technological solutions. Thus, this Special Issue represents a collection of theoretical models as well as practical case studies related to the introduction of Industry 4.0 concepts in small- and medium-sized enterprises.

The availability (and the development) of innovative approaches to quantitative analyses and the data processing are often mandatory to deeply characterize a sample and to correctly highlight the analytical target. These objectives are carried out either by simply improving a single aspect of the analytical protocol or by developing a synergy of steps (from extraction to instrumental configuration to chemometric approaches) to obtain the maximum analytical information sought. Examples are innovative extraction protocols (also following the recent guidelines on green analytical chemistry) or new materials for the selective extraction of target compounds, multi-analytes screening methods, and "untargeted" approaches for food applications. In this text, the various articles are attributable to these elements, in particular, we start with a multi-analyte method for the determination of 10 different cannabinoids from Cannabis sativa L. by means of conventional techniques (Mandrioli and coworkers), to then see the application of techniques hyphenated "ultra-fast" by UPLC-MS for the authentication of food products (Xue and coworkers). The work of Song and coworkers on these applications in food products is also interesting, as it highlights how the collection process (and the timing of this passage) can affect the chemical profile and, consequently, the biological activity of Panax ginseng. Mocan and coworkers, applying an innovative extraction technique based on microwaves and applying well-known, robust, and easy-to-use instrumentation, have demonstrated how it is possible to discriminate between various species of Galium and how the chemical profiles obtained can support the biological activities observed. Similarly, but with the aim of developing new sample pretreatment procedures, Maggira and collaborators have developed graphene oxide-based materials for the selective extraction of sulfonamides in milk. Shen and coworkers apply a different type of approach, the "untargeted" one, for the geographical characterization of the Gentian Rigescens for which they combine chemometric techniques for the processing of raw chemical profile data. Wang and coworkers report a multiclass screening of drugs with high-resolution mass spectrometry through which they manage to obtain a high-scale, fast screening method for pesticides in fishery drugs based on ultrahigh-performance liquid chromatography tandem quadrupole-orbitrap high-resolution mass spectrometer.

Sustainable value management reveals a new space for studying business models. The traditional approach is based on the assumption that the goal of any business is to make money. All decisions regarding supply and production should be made to maximize profit. The discrepancy in creating non-economic value is sometimes the result of separating ownership from control over an enterprise. Although shareholders are interested in maximizing profit, management that actually makes decisions can also pursue other goals. In addition to economic aspects, the management intentions of modern managers are also influenced by factors arising from the organizational culture built, co-created within the organization and sometimes with the participation of external actors such as suppliers and customers. The sources of the creation of social values will be the management intentions of top management, often initiated by the adopted values and rules on the basis of which resources are bound within the structure of the business model. The value of sustainability is based on the identification of those creative sources that relate to economic and social value. Economic value is created through social value and vice versa. This allows the complementarity of the value created to be mutually supportive. The business model that integrates both of these values should be more resistant to crises than the one that is oriented only toward producing economic value. Concurrent implementation of economic and social goals increases resilience and affects the success of modern business models. This is due to the specificity of the business ecosystem that is built as part of the business model, which, in essence, is based on the use of social factors to merge the business model into a complex ecosystem capable of producing value.

Nutraceuticals are a challenge for the future of prevention and therapy in healthcare. The possibility to prevent and/or support pharmacological therapy, which is nowadays mainly based on pharmaceuticals, can be a powerful tool to face pathological, chronic, long-term diseases in subjects who do not qualify for a pharmacological therapy. Nutraceuticals are obtained from vegetal or animal origin foods, and prospective research on these products will clarify their role, safety and efficacy by substantiating their role with clinical data. An effort to clarify their mechanism of action will open a door to the next generation of therapeutic agents that do not propose themselves as an alternative to drugs, but, instead, can be helpful to complement a pharmacological therapy, and to prevent the onset of chronical diseases. The market as well as the interest of people in naturally-derived remedies and less synthetic pharmaceuticals is growing, and the attention of the collective public imagination is nowadays more strongly focused on these food-derived products. This Special Issue is dedicated to the role of and perspectives on nutraceuticals in human health, examined from different angles ranging from analytical aspects to clinical trials, and from efficacy studies to beneficial effects on health conditions.

Salt (NaCl) is a key component of the human diet because it provides the sodium ion (Na+), an essential mineral for our body. Na+ regulates extracellular fluid volume and plays a key role in many physiological processes, such as the generation of nerve impulses. Na+ is lost continuously through the kidneys, intestine, and sweating. Thus, to maintain proper bodily balance, losses have to be balanced with foods containing this cation. The need for salt explains our ability to detect Na+ in foodstuffs: Na+ elicits a specific taste sensation called "salty", and gustatory sensitivity to this cation is crucial for regulating its intake. Indeed, the widespread use of salt in food products for flavoring and to improve their palatability exploits our sense of taste for Na+. When consumed in excess, however, salt might be detrimental to health because it may determine an increase in blood pressure-a major risk factor for many cardiovascular diseases. Understanding how salt taste works and how it affects food preference and consumption is therefore of paramount importance for improving human nutrition. This book comprises cutting-edge research dealing with salt taste mechanisms relevant for nutrition and health.

Disordered proteins are relatively recent newcomers in protein science. They were first described in detail by Wright and Dyson, in their J. Mol. Biol. paper in 1999. First, it was generally thought for more than a decade that disordered proteins or disordered parts of proteins have different amino acid compositions than folded proteins, and various prediction methods were developed based on this principle. These methods were suitable for distinguishing between the disordered (unstructured) and structured proteins known at that time. In addition, they could predict the site where a folded protein binds to the disordered part of a protein, shaping the latter into a well-defined 3D structure. Recently, however, evidence has emerged for a new type of disordered protein family whose members can undergo coupled folding and binding without the involvement of any folded proteins. Instead, they interact with each other, stabilizing their structure via "mutual synergistic folding" and, surprisingly, they exhibit the same residue composition as the folded protein. Increasingly more examples have been found where disordered proteins interact with non-protein macromolecules, adding to the already large variety of protein-protein interactions. There is also a very new phenomenon when proteins are involved in phase separation, which can represent a weak but functionally important macromolecular interaction. These phenomena are presented and discussed in the chapters of this book.

The management of cultural heritage and public real-estate assets is one of the most crucial challenges concerning the sustainable use of these resources, involving dynamic methods to stimulate preservation, development, renewal, and transmission to future generations of these essential assets. The contributions presented in this book provide a rich and varied panorama of research experiences and innovative tools, capable of promoting the re-use of cultural heritage in European cities and cultural landscapes, using a circular economy logic as a model of sustainable development. From this point of view, cultural capital becomes the driver of a regeneration process on the local, urban, and metropolitan scales, in which the transversal interconnections between the production cycles of the adaptive re-use of the available heritage, both in the adaptation and in the management phase, configure a circular process of multidimensional production of value. Therefore, future territorial redevelopment projects can base their idea strength on an open system of appropriately selected social attractors, whose enhancement and use have the objective of triggering widespread regeneration effects on the whole territory of influence, receiving inducement and resources to progress.

The world of laser matter interaction has known great and rapid advancements in the last few years, with a considerable increase in the number of both experimental and theoretical studies. The classical paradigm used to describe the dynamics of laser produced plasmas has been challenged by new peculiar phenomena observed experimentally, like plasma particles'' oscillations, plume splitting and self-structuring behavior during the expansion of the ejected particles. The use of multiple complementary techniques has become a requirement nowadays, as different aspects can be showcased by specific experimental approaches. To balance these non-linear effects and still remain tributary to the classical theoretical, views on laser produced plasma dynamics novel theoretical models that cover the two sides of the ablation plasma (differentiability and non-differentiability) still need to be developed. Plasma is a strongly nonlinear dynamic system, with many degrees of freedom and other symmetries, favorable for the development of ordered structures, instabilities and transitions (from ordered to chaotic states). In such contexts, we showcased research based on global and local symmetries, complexity and invariance. This special number highlighted exciting new phenomena related to laser produced plasma dynamics with the implementation of theoretical models, towards understanding the complex reality of laser matter interaction.

ROS were long considered one of the key players in tissue injury. Indeed, overproduction of ROS results in oxidative stress, a process leading to the development of many pathological conditions. For the treatment of these conditions, the use of antioxidants was proposed. Over time, it was shown that ROS at low concentrations act as signaling molecules, leading to the regulation of physiological functions. Moreover, several interventions that increase ROS generation activate stress-adaptive responses that extend the lifespan. It was also shown that excessive use of antioxidants can counter the beneficial effects of ROS. Currently, much progress has been made in understanding the role of ROS in human diseases and aging, as well as in the regulation of physiological functions, and in identifying the signaling pathways involved in ROS. However, much remains to be understood about the mutual interactions among signaling pathways underlying organisms'' adaptive responses, their modifications (which occur during aging), and some disease states. The aim of this Special Issue is to underline the effects of ROS production and antioxidant treatment in living organisms, focusing on their impact on health, disease, and aging.

Electromagnetic (EM) waves carry energy through propagation in space. This radiation associates with entangled electric and magnetic fields which must exist simultaneously. Although all EM waves travel at the speed of light in vacuum, they cover a wide range of frequencies called the EM spectrum. The various portions of the EM spectrum are referred to by various names based on their different attributes in the emission, transmission, and absorption of the corresponding waves and also based on their different practical applications. There are no certain boundaries separating these various portions, and the ranges tend to overlap. Overall, the EM spectrum, from the lowest to the highest frequency (longest to shortest wavelength) contains the following waves: radio frequency (RF), microwaves, millimeter waves, terahertz, infrared, visible light, ultraviolet, X-rays, and gamma rays. This Special Issue consists of sixteen papers covering a broad range of topics related to the applications of EM waves, from the design of filters and antennas for wireless communications to biomedical imaging and sensing and beyond.

Migration has become a structural part of the globalized society in which we live and, as such, it is essential to determine the causes and effects it produces in the involved social groups. Sociolinguistics has a very important role to play in this respect, insofar as its object of study focuses precisely on the analysis of the interrelationships between the linguistic and the social dimensions. This volume presents a series of proposals that involve theoretical approaches, models, and applications related to the process of sociolinguistic integration in contact situations arising from migration. The volume includes studies of general interest which present models and theoretical foundations for the analysis of this process of integration, as well as others which focus on other more specific aspects, such as how migration influences the construction of individual identity, emotional and affective factors in the preservation of the heritage language, and the processes of interlingual convergence that take place in situations of migratory contact. This volume also contains the didactic dimension applied to the immigrant population, with proposals for teaching with proven effectiveness.

Nonequilibrium statistical mechanics has a long history featuring diverse aspects. It has been a major research field in physics and will remain so in the future. Even regarding the concept of entropy, there exists a longstanding problem concerning its definition for a system in a state far from equilibrium. In this Special Issue, we offered the possibility to discuss and present up-to-date problems that were not necessarily restricted to statistical mechanics. Theoretical and experimental papers are both presented, in addition to unifying research works. As the entropy itself is the central element of nonequilibrium processes, papers discuss various formulations of the second law and its consequences. In this Special Issue, recent progress in kinetic approaches to hydrodynamics, rational extended thermodynamics, entropy in a strongly nonequilibrium stationary state, and related topics are reported as both review articles as well as original research works.

Catalysis, in the industrial production of chemicals, fuels, and materials, accounts for more than half of gross material production worldwide. Heterogeneous catalysis enables fast and selective chemical transformations, resulting in superior product yield and facilitating catalyst separation and recovery. The synthesis of novel catalysts has emerged as a hot topic for process and product development with numerous research publications and patents. Hence, development of efficient catalysts and their applications is important for sustainable energy production and use, green chemicals production and use, and economic growth. This Special Issue discusses recent developments related to catalysis for the production of sustainable fuels and chemicals and traverses many new frontiers of catalysis including synthesis, characterization, catalytic performances, reaction kinetics and modelling, as well as applications of catalysts for the production of biofuels, synthesis gas, and other green products. This covers the current state-of-the-art catalysis research applied to bioenergy, organic transformation, carbon-carbon and carbon-heteroatoms, reforming, hydrogenation, hydrodesulfurization, hydrodenitrogenation, hydrodemetalization, Fischer-Tropsch synthesis, to name a few. This book highlights new avenues in catalysis including catalyst preparation methods, analytical tools for catalyst characterization, and techno-economic assessment to enhance a chemical or biological transformation process using catalysts for a betterment of industry, academia and society.

Photovoltaic (PV) cells, which directly convert sunlight into electricity, are renewable sources of energy that are sustainable and totally inexhaustible. Emerging classes of solar PV cells have drawn considerable attention because they provide significant advantages over traditional silicon solar cells, such as low cost and attractive designs (lightweight, flexible, and portable) while exhibiting promising performance. Despite these features, certain challenges restrict the possible commercialization of these technologies. The world''s leading scientists are making numerous efforts focused on bringing these promising technologies closer to commercialization. Some of these scientists provided valuable research contributions to this Special Issue on "Advances in Emerging Solar Cells" published by Nanomaterials, MDPI. This Special Issue presents 12 excellent articles, 10 research and 2 review papers, covering perovskite solar cells, heterojunction solar cells, organic solar cells, dye-sensitized solar cells, and PV materials. We think that this Special Issue will attract significant attention from a broad research community including renewable energy, photovoltaic, emerging solar cells, material science and nanotechnology.

This eBook focuses on current progress in understanding the role of chromatin structure, its modifications and remodeling in developmental and physiological processes. Eukaryotic genomes are packed into the supramolecular nucleoprotein structure of chromatin. Therefore, our understanding of processes such as DNA replication and repair, transcription, and cell differentiation requires an understanding of the structure and function of chromatin. While the nucleotide sequence of the DNA component of chromatin constitutes the genetic material of the cell, the other chromatin components (and also modifications of bases in the DNA itself) participate in so-called epigenetic processes. These processes are essential, e.g., in ontogenesis or adaptation to environmental changes. Therefore, epigenetics is particularly important (and elaborated) in plants that show a high developmental plasticity and, as sessile organisms, display an enormous capacity to cope with environmental stress. In these processes, epigenetic mechanisms show a crosstalk with plant signaling pathways mediated by phytohormones and redox components. You are welcome to read examples of current research and review articles in this hot research topic.

The agricultural community is face with the challenge of increasing food production by more than 70% to meet demand from the global population increase by the mid-21st century. Sustainable food production involves the sustained availability of resources, such as water and energy, to agriculture. The key challenges to sustainable food production are population increase, increasing demands for food, climate change, climate variability, and decreasing per capita land and water resources. To discuss more details on (a) the challenges for sustainable food production and (b) mitigation options available, a Special Issue on "Water Management for Sustainable Food Production" was assembled. This Special Issue focused on issues such as irrigation using brackish water, virtual water trade, allocation of water resources, consequences of excess precipitation on crop yields, strategies to increase water productivity, rainwater harvesting, irrigation water management, deficit irrigation, fertilization, environmental and socio-economic impacts, and irrigation water quality. The articles in the Special Issue cover several water-related issues across the U.S., Asia, Middle East, Africa, and Pakistan concerning sustainable food production. The articles in this Special Issue highlight the substantial impacts on agricultural production, water availability, and water quality in the face of increasing demands for food and energy.

Antiviral agents are used for the treatment of viral diseases. Antiviral drugs have been successfully developed and used clinically for a limited number of important human viral diseases notably caused by human immunodeficiency virus (HIV), hepatitis C virus (HCV), hepatitis B virus (HBV), herpes, and influenza viruses. Despite the successes of these antiviral drugs, issues with drug resistance and toxicity remain challenging. These challenges are driving research to identify new drug candidates and to investigate novel drug targets to develop new mechanistic drug classes. Antiviral agents are not available against many viruses that cause human disease and economic burdens; in particular, the development of antiviral agents against emerging, re-emerging, and neglected viruses is increasingly becoming a priority. This book includes six review articles that discuss new antiviral strategies. The reviews either discuss advances relating to a specific virus or new therapeutic targets and approaches. The book includes 15 original research articles reporting new antiviral agents against a variety of clinically and economically important viruses and studies into the prevalence or acquisition of drug resistance. Overall, this book is an exciting collection of new research and ideas relating to the development of antiviral agents.

This Special Issue comprises selected papers from the proceedings of the 5th International Electronic Conference on Sensors and Applications, held on 15-30 November 2018, on sciforum.net, an online platform for hosting scholarly e-conferences and discussion groups. In this 5th edition of the electronic conference, contributors were invited to provide papers and presentations from the field of sensors and applications at large, resulting in a wide variety of excellent submissions and topic areas. Papers which attracted the most interest on the web or that provided a particularly innovative contribution were selected for publication in this collection. These peer-reviewed papers are published with the aim of rapid and wide dissemination of research results, developments, and applications. We hope this conference series will grow rapidly in the future and become recognized as a new way and venue by which to (electronically) present new developments related to the field of sensors and their applications.

Improved understanding of the cellular and molecular makeup of tumors in the last 30 years has unraveled a previously unexpected level of heterogeneity among tumor cells as well as within the tumor microenvironment. The concept of tumor heterogeneity underlines the realization that different tumors can display significant differences in their genomic content as well as in their overall behavior. Our capacity to better understand the heterogeneous make up of tumors has very important consequences on our ability to design efficient therapeutic strategies to improve patient survival. This book highlights several aspects of tumor heterogeneity in the context of metastatic development and summarize some of the challenges posed by heterogeneity for tumor diagnostics and therapeutic management of tumors.