The estrogen receptors are members of a large family of transcription factors, which include receptors for steroid hormones, retinoids, vitamin D and thyroid hormone, as well as several orphan receptors with yet undiscovered ligands. The process by which small lipophilic molecules signal in target tissues is complex and involves nuclear receptor associations with a multitude of coregulator proteins. These proteins participate in and recruit many enzymatic and structural activities that allow modulation of chromatin structure to facilitate stimulation or repression of gene expression. This review will present an overview of those regulatory factors that interact with the estrogen receptors and participate in the transmission of the estrogenic signal.