The two oestrogen receptor subtypes α and β are hormone-regulated modulators of intracellular signalling and gene expression. Regulation of oestrogen receptor activity is crucial not only for development and homeostasis but also for the treatment of various diseases and symptoms. Classical selective oestrogen receptor modulators are well established in the treatment of breast cancer and osteoporosis, but emerging data suggest that the development of subtype-selective ligands that specifically target either oestrogen receptor-α or oestrogen receptor-β could be a more optimal approach for the treatment of cancer, cardiovascular disease, multiple sclerosis and Alzheimer's disease.