The rise of the neutral theory of evolution has aroused a renewed interest in the quantitative approach to population genetics, and the aim of this book is to explain this field to biologists with a limited amount of mathematical expertise. The text concentrates almost entirely on stochastic processes, as these seem to be the greatest source of difficulty amongst non-mathematicians. To enhance the flow of the text some points of detail have been placed in notes and exercises sections at the end of each chapter. The material is extensively referenced and contains many carefully worked examples of mathematical proofs.