The anterior pituitary is derived from Rathke's pouch arising from the oral ectoderm. The initial apparently uniform precursor cells proliferate and differentiate into six different cell types that are present in mature gland by integrative interactions between different signaling molecules and transcription factors. This system provides an opportunity to understand gene regulation in the cellular processes of precursor cell proliferation, determination, and differentiation events during organogenesis. Recent studies have made significant advances in our appreciation of the molecular mechanisms by which transcription factors regulate these cellular processes.