HMG-CoA (or 3-hydroxy-3-methylglutaryl-coenzyme A) is an intermediate in the mevalonate and ketogenesis pathways. It is formed from acetyl CoA and acetoacetyl CoA by HMG-CoA synthase. The researches of Minor J. Coon and Bimal Kumar Bachhawat in the 1950s at University of Illinois led to its discovery.
It is also an intermediate in the metabolism of leucine. Its immediate precursor is 3-methylglutaconyl CoA.