Oestrogen receptors (ER) are emerging as important molecules involved in the variety of physiological and pathological activities. There are two classic oestrogen receptors: alpha and beta. Different cells and tissues have shown divergent responses to these two oestrogen receptors. While we are starting to understand the interaction between oestrogen receptors and its ligands contributes to the development of various diseases, the discovery of sub-isoforms of oestrogen receptor alpha and beta has further complicated the mechanism of oestrogen receptors. Nevertheless, continuing efforts in the study of oestrogen receptors have helped us to define their roles in diseases and to develop novel therapies against these disorders. The 11 chapters in this book are the excellent evidence to summarise our efforts in this direction. This book should be of great value to not only clinicians and medical students interested in oestrogen/ER-related diseases but also basic scientists working in the field of estrogens/ERs.