Histone acetylation is closely linked to gene transcription. The identification of histone acetyltransferases (HATs) and the large multiprotein complexes in which they reside has yielded important insights into how these enzymes regulate transcription. The demonstration that HAT complexes interact with sequence-specific activator proteins illustrates how these complexes target specific genes. In addition to histones, some HATs can acetylate non-histone proteins suggesting multiple roles for these enzymes.