The quadrupling of the world population in the 20th century has over-burdened the environment and accelerated the depletion of natural resources, whether renewable or not. The effort of the largest nations, China, India, and others, to attain affluence at this time further damages the environment and tax resources. Recently, fertility rates have fallen dramatically, below replacement in much of the world. The number of workers will be declining while the number elderly dependent on their support will be rising. Prospects for affluence are grim for rich and poor nations alike. There is no historical precedent for such a decline in fertility which, except in China, is a voluntary response to urbanisation, education, the liberation of women, and birth control technology. What does the future hold? This book consists of 33 essays on the 21st century problems of overpopulation and low fertility and possible policy choices.