This book provides the first compilation of demographic research focused on transgender, nonbinary, and gender minority populations. It discusses the measurement and conceptualization challenges that shape demographic knowledge of these populations, including how we capture gender on surveys. It examines our current knowledge of demographic characteristics and health disparities and outcomes. Overall, this research demonstrates the increasing knowledge of gender variation at the population level. At the same time, it reveals the need for better survey questions, additional data, and inquiry into a broader subset of demographic questions for these populations as there is little understanding of fundamental demographic information, including migration or spatial distribution of transgender populations, fertility and household structure, labor market outcomes, or broader patterns of morbidity and mortality. The research set forth in this book lays the groundwork for a trans demography that would produce population-level knowledge of these populations and points researchers and policymakers toward needed areas of research, conceptualization, and data collection.