Estrogen receptors (ER) are members of the steroid/thyroid hormone receptor uperfamily of ligand-activated transcription factors. Estrogen receptors, ncluding ERα and ERβ, contain DNA binding and ligand binding domains nd are critically involved in regulating the normal function of reproductive issues. ERα and ERβ have been shown to be differentially activated by various igands. Receptor-ligand interactions trigger a cascade of events, including issociation from heat shock proteins, receptor dimerization, phosphorylation nd the association of the hormone activated receptor with specific regulatory lements in target genes. Evidence suggests that ERα and ERβ may be egulated by distinct mechanisms even though they share many functional characteristics.