Primary cilia are solitary, generally non-motile, hair-like protrusions that extend from the surface of cells between cell divisions. Defects in primary cilia formation and function result in many developmental diseases and some adult ciliopathies. In this lecture, I will discuss the function of primary cilia in neurons, glia, kidney, and cell lines. The focus will be on measurements of ion currents in primary cilia, their underlying physiology, and the structures of these channels.