Potassium channels are a diverse group of ion channels present in most eukaryotic cells that have been examined. Over 30 different potassium channels have been characterized biophysically. They show different sensitivities to voltage and/or intracellular messengers, and have different kinetic or pharmacological properties. The wide range of potassium channel properties reflects the broad spectrum of cellular functions that they serve, including control of synaptic efficacy, of heart beat, and of endocrine and exocrine secretion. How might this tremendous diversity of potassium channels be generated? Partial answers have begun to emerge as molecular studies of potassium channel genes have become possible over the past few years.