In this paper, we develop an alternate formulation of the electron–photon interaction in the framework of ordinary relativistic quantum mechanics (without second quantization). We use the Dirac equation of motion to recast the current density in a form linear in the photon wave function. This enables us to take the photon as the system and, regarding the electron as an ’’external field,’’ to iterate the photon wave equation by the standard method. In particular, we deduce the second‐order matrix elements of Compton scattering, pair annihilation, and pair creation. The results so obtained are, of course, identical with those of the usual formulation, where the electron is taken as the system and the radiation is treated as the external field. The present approach complements the usual one; together, the two approaches reveal the symmetry of quantum electrodynamics under interchange of source and field.