ATP-sensitive potassium channels (KATP channels) play important roles in various tissues under physiological and pathophysiological conditions by coupling cell metabolic status to electrical activity. The KATP channe l is a tetrameric complex of inwardly rectified potassium (Kir) and ATP binding protein (ABP). The Kir subunits form the channel pore, whereas ABP is required for activation and regulation. Both Kir and ABP are divided into different subu nits and the various Kir and ABP subunits “mix and match” to form KATP c hannels with different pharmacological and nucleotide sensitivities. This revie w focuses on the molecular structure, physiological roles, pathophysiological an d pharmacological properties of KATP channels in different tissues.