We have investigated the phase formation sequence for the reaction of Nb and Al in multilayer films using cross‐sectional transmission electron microscopy and x‐ray diffraction. NbAl3is the first intermetallic phase to form. Contrary to previous reports, we find evidence from cross‐sectional transmission electron microscopy that the sigma phase, Nb2Al, is not bypassed in the reaction sequence. Instead, its formation is concurrent with the formation of the superconductingA15 phase, Nb3Al. However, depending on the periodicity and the composition of the film, the Nb2Al phase can be consumed by the Nb3Al phase for long annealing times. The significance of this phase formation sequence to powder metallurgically processed magnet wire is discussed.