A fuel cell stack comprises a plurality of modules and each module comprises an elongate hollow member and one passage extending through the hollow member for the flow of a reactant. Each hollow member has a first flat surface and a second flat surface. At least one of the modules includes a plurality of fuel cells arranged on at least one of the first and second flat surfaces. Each module has a first and second integral feature to provide a spacer and a connection with its adjacent modules. The first integral feature comprises a third flat surface and the second integral feature comprises a fourth flat surface. The third flat surface is arranged at an intersecting angle to the first flat surface and the fourth flat surface is arranged at an intersecting angle to the second flat surface.