Statins are the most-effective therapy currently available for lowering the LDL-cholesterol (LDL-C) level and preventing cardiovascular events. Additional therapies are necessary for patients who cannot reach the target LDL-C level when taking the maximum-tolerated dose of a statin. Proprotein convertase subtilisin/kexin type 9 (PCSK9) is an enzyme with an important role in lipoprotein metabolism. Rare gain-of-function mutations in PCSK9 lead to a high LDL-C level and premature coronary heart disease, whereas loss-of-function variants lead to a low LDL-C level and a reduced incidence of coronary heart disease. Furthermore, the PCSK9 level is increased with statin therapy through negative feedback, which promotes LDL-receptor degradation and decreases the efficacy of LDL-C lowering with statins. PCSK9 inhibition is, therefore, a rational therapeutic target, and several approaches are being pursued. In phase I, II, and III trials, inhibition of PCSK9 with monoclonal antibodies has produced an additional 50-60% decrease in the LDL-C level when used in combination with statin therapy, compared with statin monotherapy. In short-term trials, PCSK9 inhibitors were well tolerated and had a low incidence of adverse effects. Ongoing phase III trials will provide information about the long-term safety of these drugs, and their efficacy in preventing cardiovascular events.