The role of carnitine via the action of carnitine acyltransferase in buffering CoA availability in the mitochondrial matrix is well known. There is now sufficient evidence to extend this to a general role. Carnitine can buffer the acylation state of the CoA pool for any type of acyl group that is a substrate for the carnitine acyltransferase family of enzymes. Specific carnitine acyltransferases in each organelle or membrane can modulate the reserves of free CoA and acyl-CoA in ways specific to the local metabolic demands. The use of inhibitors of carnitine acyltransferases in complex systems and in vivo now permits exploration of the consequences of this role.