For a number of years, high-density lipoprotein (HDL) has been recognized to have an athero-protective role by promoting reverse lipid transport, a process facilitating the cholesterol efflux from atherosclerotic plaques in the artery wall and its elimination by the liver via biliary excretion. On the contrary, low-density lipoprotein (LDL) particles carry cholesterol to the organs and tissues where it can be used to produce hormones or maintain cell metabolism. When an imbalance develops, as a result of either an excess level of cholesterol associated with LDL (LDL-C) or a less effective cholesterol elimination by HDL (HDL-C), this causes an excess of cholesterol to be transported to the tissues and promotes the deposition of cholesterol. This often occurs in the artery walls, particularly in the coronary arteries. There is no approved medical treatment for directly suppressing or treating the atherosclerotic plaque once it is formed. Epidemiological studies have shown that the risk of developing cardio-vascular disease (CVD) is higher in patients with low levels of HDL-C regardless of LDL-C levels, even in patients optimally treated with LDL-C-lowering therapies. These data highlight that low HDL-C and low HDL particle number is an important target of therapies aiming to reduce the residual risk of CVD.