The introduction of new “designer estrogen” compounds into clinical practice and research has stimulated interest in osteoporosis and global estrogen action. These agents are being developed clinically to address bone, central nervous system, and cardiovascular health and as preventives or therapeutics for hormone-dependent cancers. This brief review focuses on recent advances in the complex biochemistry of estrogen and estrogen receptor modulators, the comparative chemistry of such agents, and the clinical consequences of their administration to women. Although the appropriate use of these agents in bone loss prevention and treatment is still unclear, they are a valuable alternative for women who cannot or will not take estrogen or bisphosphonates and are at risk for the disease. Newer agents in this class currently under development promise improved selectivity and potency, and may well provide additional therapeutic options for bone health, breast diseases, and other disorders.