This volume is a collection of papers designed to increase awareness and utilization of fluctuation theory for the description of ionic events at the membrane. The papers are revised and updated versions of presentations made at a workshop entitled "Noise Measurements as a Probe of Ionic Conductance. " As a result of discussions held at that meeting, the participants were asked to provide selected chapters designed to provide detailed descriptions of the theory and its application to a number of membrane channels. Fluctuation theory was developed initially to explain statistical fluctuations...