The book is a collection of selected articles by A. G. Vishnevsky, published mainly over the last 10-15 years and dedicated to key issues of demography of the 21st century. The main attention in the articles selected for publication is focused on the theoretical understanding of fundamental events occurring in the world demographic changes and the consequences they cause. These consequences are universal and permeate all levels of social reality, from the family to the global. Russian issues occupy an important place in the book; the author seeks to understand the demographic changes Russia is experiencing and the demographic challenges it faces in the context of universal and global demographic changes and challenges. Some of the articles are devoted to the history and current state of domestic demographic science. The potential audience of the book is researchers representing a wide range of social science disciplines, teachers and students, politicians and journalists, as well as readers interested in demography and related sciences. The publication of the book is dedicated to the 80th anniversary of A. G. Vishnevsky.