Atazanavir is a recently approved human immunodeficiency virus (HIV) protease inhibitor that has an important role in the treatment of both antiretroviral-naive and antiretroviral-experienced individuals. Atazanavir (400 mg) can be administered once per day and requires only 2 capsules. Drug exposure can be safely increased with coadministration of a once-daily regimen of atazanavir (300 mg) and ritonavir (100 mg). Atazanavir is not associated with elevations in serum levels of total cholesterol, low-density lipoprotein cholesterol, or triglycerides, potentially reducing the need for lipid-lowering agents. Atazanavir is associated with elevations in unconjugated bilirubin levels, which are usually not dose limiting. For treatment-naive patients receiving atazanavir who experience virologic rebound, the I50L mutation in HIV protease arises, which does not confer cross-resistance to other protease inhibitors. In treatment-experienced patients with high-level resistance to other protease inhibitors, susceptibility to atazanavir is usually reduced, and optimal effects of atazanavir are seen when it is administered with ritonavir. Similar to other protease inhibitors, careful attention must be paid to drug interactions when administering atazanavir with concomitant medications.