Histone acetyltransferases (HATs) are essential enzymes that are, among others, involved in the epigenetic regulation of gene transcription. They exert their functions through acetylation of both histone and nonhistone proteins and are often part of multiprotein complexes. This chapter mainly discusses recent studies on the functions of HATs in diseases and their utility as potential drug targets. Furthermore, this chapter describes the recent progress in the development of small-molecule HAT modulators and their therapeutic potential. Dysregulation of HAT-mediated acetylation of histone and nonhistone proteins contributes to the pathogenesis and progression of many diseases, such as cancers, inflammatory diseases, and neurological disorder...