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A composite electrode has a surface that consists of an ordered arrangement (array) or a random arrangement (ensemble) of conductor regions, typically micrometers in dimension, separated from one another by an insulator. These active regions (or microelectrodes) may themselves be of regular geometry and confined primarily to the surface, as with most array electrodes, or of irregular geometry and permeate the bulk of the material, as with most ensemble electrodes. In this review, we classify composite electrodes according to the distribution of a conductor and insulator within the material (or on the surface), survey a number of the fabrication schemes used to construct composite electrodes, discuss percolation theory as it applies to certain composite electrodes, examine the surface morphology of selected composite materials, discuss the origins of the enhancement in current density observed at many composite electrodes in both quiescent and flowing solutions, and provide a few examples illustrating the applications of composite electrodes t o real analytical problems.