The Trinidadian guppy is well known to biologists and home aquarium enthusiasts alike. This book describes the sexual behaviour of guppies, and examines how mate choice by females leads to the evolution of the conspicuous colours and the courtship displays for which guppies are widely recognized. It shows that female guppies prefer males with bright colour patterns, especially those with orange spots, and that the mating preferences of females lead to a sexual selection of both colour patterns and courtship displays of males.