The orphan receptor estrogen-related receptor alpha (ERR alpha) is a member of the nuclear receptor superfamily of ligand-regulated transcription factors. This protein is structurally most related to the canonical estrogen receptor and has been shown to modulate estrogen signaling in some contexts. These observations have heightened interest in ERR alpha as a therapeutic target in both breast and ovarian cancer and in other estrogenopathies. This review details our present understanding of ERR alpha action with a view to highlight specific aspects of its signal-transduction pathway in breast cancer that may be amenable to pharmaceutical manipulation.