A fuel cell system comprising a fuel cell stack and a layer assembly forming the fluid circuitry for the fuel cell stack. The layer assembly comprises a plurality of layers assembled in face-to-face contact and joined together in a fluid-tight manner. At least some of the layers integrate fluid-interacting devices and/or fluid-conveying channels. The layers have aligned openings for forming potential passageways through the layer assembly, and these passageways are partially opened and/or partially blocked to form the fluid circuitry.