High-density lipoprotein (HDL) is the particle that carries cholesterol away from the tissues and artery walls back to the liver for disposal — the “good cholesterol” of popular language. These small, dense aggregates of protein and fat scavenge excess cholesterol in a process called reverse cholesterol transport, and high HDL levels are associated with lower risk of coronary heart disease. Exercise, moderate alcohol intake, and unsaturated fats tend to raise HDL; smoking, obesity, and trans fats lower it. But the story has grown subtler: drugs that raise HDL have failed to prevent heart attacks, suggesting that HDL’s function matters more than its quantity. Clinicians interpret HDL alongside LDL cholesterol and triglycerides, never in isolation.