This an updated version of a book which is revered for its direct, clear approach. It is aimed at students taking their first course in biological statistics and for biologists handling data mathematically. There are many elementary statistical textbooks but this book is unique in its concern with underlying ideas, with how to choose the right method for the right question, and with how to avoid common pitfalls. Unlike other texts, it answers the questions most often asked by biologists, discusses the aspects of biology which rely heavily on mathematics, and emphasizes practical applications, including when not to use statistical methods. This second edition has been thoroughly revised and updated, with completely rewritten chapters on quantitative genetics and population ecology. Although it was originally intended to be supplementary reading for biologists who already know the elements of statistics, it has stood the test of time and proven itself to be an effective learning aid in the classroom as well.