The primary endocrine organs responsible for steroid hormone biosynthesis--the adrenal cortex and gonads--are derived from the urogenital ridge. Several recent discoveries in human and mouse genetics have begun to unravel the complex genetic cascade that dictates adrenocortical cell lineage, proliferation and differentiation. The factors that regulate adrenocortical organogenesis and the maintenance of growth promote or block a cascade of transcription factors that differentially coordinate the proliferation and differentiation of the gland. Here, we outline the developmental milestones of the adrenal cortex with recent contributions to the field, focusing on factors that have been shown to play a role in vivo in humans and mice.