The mechanism of tungsten alloy plating was investigated. Absorption spectra indicate the possibility of cobalt tungstate complexes in the citrate cobalt‐tungsten plating bath. Polarographic evidence is given for the existence of complexes of tungstate and citrate. Calculations of energies of activation of iron‐tungsten alloy deposition show that the tungstate reaches the cathode by diffusion rather than by migration. The mechanism postulated for the plating of tungsten alloys includes (a) the deposition of a film of partly reduced tungstate on the cathode and (b) the catalytic reduction of this film by hydrogen in the presence of freshly deposited iron, cobalt, or nickel.