Ion channels are crucial components of living cells. Situated in the cell's membranes. they allow particular ions to pass from one side of the membrane to the other. In recent years the patch clamp technique has allowed the activity of individual channels to be measured, and recombinant DNA technology has led to fascinating detail on their structure. Together, these technical advances have produced a great flowering of knowledge and understanding about the subject, itself leading to further breakthroughs in science and medicine. Ion Channels provides an introduction to this scientific endeavour. It emphasises the molecular structure of channels as determined by gene cloning technology. This knowledge illuminates discussions of the permeability and selectivity of channels, their gating and modulation, their responses to drugs and toxins and the human diseases caused when they do not function properly.