According to the classic and widely accepted statement by Hauser and Duncan (1959: 2), demography is defined as “the study of the size, territorial distribution, and components of population, changes therein, and components of such changes.” Almost all disciplines of social sciences and most disciplines of natural sciences deal with human beings in one way or another, either directly or indirectly. Furthermore, demographic concepts (e.g., birth rate, death rate, and migration) and methods and analysis strategies (e.g., life table analysis) can be readily extended to other species (insects, animals, plants, etc.) and inanimate collectives (enterprises, automobiles, etc.). Clearly, demography is an important thematic field in science and it may provide the empirical foundation for studying human beings, animals, and inanimate collectives on which other relevant scientific research is built. The volume aims to be of value to the various audiences of both non-specialists and experts who seek a comprehensive understanding of issues related to human population. As reviewed in the very beginning of the Theme Introduction, “interdisciplinary” is one of the three major features of demography. Given the rapid development in techniques for collecting not only demographic data but also other related data concerning health, biomarkers, genetics, behaviors, and social and natural environments in conventional population surveys, as well as rapidly enhancing computing powers, this volume shows and concludes that demography will be even more interdisciplinary in the coming decades. A notable example is that the cross-field “marriage” between bio-medical sciences and demography will lead us to enter an era in which bio-medical and demographic methods will be well integrated. As indicated by James R. Carey and James W. Vaupel in Chapter 13 of this volume, the bio-demographic branches of demography are vibrant areas of demographic research that are rapidly growing and that have great potential to enrich and enlarge the domain of demography. Not only can demographers learn much from biologists and epidemiologists, but demographers can contribute much to research on life in general and to research on population health. The increasing availability of data sources and much enhanced computing/internet power will also lead demography to be more interactive with the other fields, such as psychology, environmental science, economics, business and management, etc. As discussed in this volume’s Chapter 11 by Swanson and Pol, for example, it is now possible to link conventional demographic data sources of census, surveys, and vital statistics with administrative records such as social security, tax reporting, medical insurance, hospital records, school registration, supermarket purchasing cards use, etc., while protecting individuals’ privacy. Such linkages will substantially increase the value of demographic methods, surveys and administrative records for scientific research and policy analysis, as well as the applicability of demography in business and governmental decision making processes.