K⁺ channels are widely distributed in both plant and animal cells where they serve many distinct functions. K⁺ channels set the membrane potential, generate electrical signals in excitable cells, and regulate cell volume and cell movement. In renal tubule epithelial cells, K⁺ channels are not only involved in basic functions such as the generation of the cell-negative potential and the control of cell volume, but also play a uniquely important role in K⁺ secretion. Moreover, K⁺ channels participate in the regulation of vascular tone in the glomerular circulation, and they are involved in the mechanisms mediating tubuloglomerular feedback. Significant progress has been made in defining the properties of renal K⁺ channels, including their location within tubule cells, their biophysical properties, regulation, and molecular structure. Such progress has been made possible by the application of single-channel analysis and the successful cloning of K⁺ channels of renal origin.