Acetyl-CoA carboxylase (ACC) catalyses the formation of malonyl-CoA, an essential substrate for fatty acid synthesis in lipogenic tissues and a key regulatory molecule in muscle, brain and other tissues. ACC contributes importantly to the overall control of energy metabolism and has provided an important model to explore mechanisms of enzyme control and hormone action. Mammalian ACCs are multifunctional dimeric proteins (530-560 kDa) with the potential to further polymerize and engage in multiprotein complexes. The enzymatic properties of ACC are complex, especially considering the two active sites, essential catalytic biotin, the three-substrate reaction and effects of allosteric ligands. The expression of the two major isoforms and splice variants of mammalian ACC is tissue-specific and responsive to hormones and nutritional status. Key regulatory elements and cognate transcription factors are still being defined. ACC specific activity is also rapidly modulated, being increased in response to insulin and decreased following exposure of cells to catabolic hormones or environmental stress. The acute control of ACC activity is the product of integrated changes in substrate supply, allosteric ligands, the phosphorylation of multiple serine residues and interactions with other proteins. This review traces the path and implications of studies initiated with Dick Denton in Bristol in the late 1970s, through to current proteomic and other approaches that have been consistently challenging and immensely rewarding.