The main theme of Sexual Selection and the Barn Swallow is that sexual selection is important and affects many aspects of animal life such as mating behaviour, mating competition, parental care, host parasite interactions, and migration strategies. Birds with extravagant feather ornaments are the standard example of sexual selection. Here the selective advantages of a long tail are investigated for a common bird, the barn swallow, in the context of sexual selection theory. This study constitutes a major empirical test of the theoretical predictions and will be of special interest to students of behavioural and evolutionary ecology. The first two chapters present a concise, insightful review of sexual selection theory and its two main components, male-male competition and female choice. Subsequent chapters investigate the advantage for males of being extravagantly adorned and the advantages that females acquire by being choosy when selecting a mate, using evidence from the author's long-term field work on the monogamous barn swallow. Moller explores the roles of behaviour, ecology, morphology, genetics, and evolution to provide a valuable synthesis of this work to date.