This paper provides an overview, of the application of minichannels, typically on the order of a I nun hydraulic diameter, in the design of polymer electrolyte membrane (PEM) fuel cells. In these electrochemical devices, minichannels deliver reactant hydrogen and oxygen to the anode and cathode electrodes, respectively, while transporting product water out of the cell. The channels must be designed for low pressure drop to avoid excessive parasitic power losses from gas handling equipment. However, the channels also need to operate in a flow regime in which the overall water balance in the fuel cell can be maintained. The various aspects of minichannel design, including size and cross-sectional shape, are discussed, with a particular emphasis on fuel cell water management. In addition to reviewing these fundamental aspects of minichannel design, examples are given of new experimental tools currently under development that are applied to relate channel water transport and accumulation to fuel cell performance.