Owing to the high degree of similarity between aldosterone synthase (CYP11B2) and cortisol synthase (CYP11B1), the design of selective inhibitors of one or the other of these two enzymes was, at one time, thought to be impossible. Through development of novel enzyme screening assays and significant medicinal chemistry efforts, highly potent inhibitors of CYP11B2 have been identified with selectivities approaching 1000-fold between the two enzymes. Many of these molecules also possess selectivity against other steroidogenic cytochromes P450 (e.g. CYP17A1 and CYP19A1) as well as hepatic drug metabolizing P450s. Though not as well developed or explored, inhibitors of CYP11B1, with selectivities approaching 50-fold, have also been identified. The therapeutic benefits of affecting the renin-angiotensin-aldosterone system have been well established with the therapeutically useful angiotensin-converting enzymes inhibitors, angiotensin receptor blockers, and mineralocorticoid receptor antagonists. Data regarding the additional benefits of an aldosterone synthase inhibitor (ASi) are beginning to emerge from animal models and human clinical trials. Despite great promise and much progress, additional challenges still exist in the path towards development of a therapeutically useful ASi.