Fertility is the natural capability of giving life. As a measure, the "Fertility Rate" is the number of children born per couple, person or population. This is different to fecundity, which is defined as the potential for reproduction (influenced by gamete production, fertilisation and carrying a pregnancy to term). Human fertility depends on factors of nutrition, sexual behaviour, culture, instinct, endocrinology, timing, economics, way of life, and emotions. Animal fertility has no fewer complexities, and may display many interesting mechanisms. This book presents the latest research from around the world in this field.