It is widely believed that reproductive cycles are very similar between human females. However, there are in fact considerable variations both between individuals and within the reproductive life of any given individual. ‘Normal’ reproductive cycles cover a wide range of eventualities, and the likelihood of successful monthly egg release and ensuing pregnancy can be modified by a large number of factors. In this book, the variability of human fertility is examined by first looking at the physiological processes regulating reproduction, and the roles of metabolic adaptation and metabolic load. Inter-population variation in normal ovarian function is then discussed, covering the importance of factors such as age, disease and breast-feeding in modifying ovarian function. This will be an important book for all those interested in human fertility.