HMG-CoA reductase (HMGCR) is the key rate-limiting enzyme in cholesterol synthesis, located in the endoplasmic reticulum, converting HMG-CoA to mevalonate. It is expressed in various tissues, including the liver, and is the primary target of statin drugs, used to lower cholesterol levels in the blood. The activity of HMGCR is subject to feedback inhibition by cholesterol levels, regulated through mechanisms such as phosphorylation and proteolysis. Gene expression is influenced by genetic and environmental factors, with specific variants associated with the risk of cardiovascular diseases. Dysfunction or abnormal expression of HMGCR affects cholesterol homeostasis, related to various metabolic disorders.