This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book explores how population conditions can be taken into consideration in addressing problems of promoting economic development, environmental conservation or, more broadly, sustainable development. It describes how population conditions can be examined and linked to planning for environmental conservation and sustainability. The book focuses more on population, however, which implies giving much attention to the condition of rapid population growth in the Less Developed Regions. It considers a series of issues in organizing at the national level for integrating population issues with strategies for sustainable development. The book also focuses specifically on the population–environment nexus. It provides a discussion of the Demographic Transition, one of the most profound changes the human species has experienced. The book reviews basic demographic tools, as well as the course of population dynamics especially in the low income countries of the world.