More and more people are calling for wildlife managers to use 'fertility control' on superabundant populations of, for example, Canada Geese or coyotes. This book reviews that in the past, fertility control has been far less successful than observers had hoped, but thanks to new findings about animal reproductive systems, the technology is advancing rapidly and is being tested on several species on a small scale. Hurdles include the need to develop and commercialize effective vaccines or baits, cost effective delivery systems, and public agency acceptance of the technique.