This book is aimed at anyone with a serious interest in ecology. Ecological models of two kinds are dealt with: mathematical models of a strategic kind aimed at an understanding of the general properties of ecosystems and laboratory models designed with the same aim in view. The mathematical and experimental models illuminate one another. A strength of the account is that although there is a good deal of mathematics, Professor Maynard Smith has concentrated on making clear the assumptions behind the mathematics and the conclusions to be drawn. Proofs and derivations have been omitted as far as possible. The book is therefore comprehensible to anyone with a minimal familiarity with mathematical notation. This book was written in the twin convictions that ecology will not come of age until it has a sound theoretical basis and there is a long way to go before that state of affairs is reached.