Proper gas, water and thermal management is vital to the successful operation of proton-exchange-membrane fuel cells. The effectiveness of the direct liquid water injection scheme and the interdigitated flow field design towards providing optimal gas distribution, membrane hydration, and heat removal and alleviating the mass transport limitations of the reactants and electrode flooding was investigated. It was found that the direct liquid water injection used in conjunction with the interdigitated flow fields is an extremely effective method of gas, water and thermal management. When used in the anode, the forced flow-through-the-electrode characteristic of the interdigitated flow field provides higher transport rates of reactant from the flow channels to the inner catalyst layer, increases the hydration state and conductivity of the membrane by bringing its anode/membrane interface in direct contact with liquid water, and increases the cell tolerance limits for excess injected liquid water, which could be used to provide simultaneous evaporative cooling for the cell. When used in the cathode, in addition to the enhanced transport rate of gaseous reactant and product, the shear force of gas flow through the electrode helps to remove the liquid water that is entrapped in the inner layers of the electrode, thereby significantly reducing the electrode flooding problem.