The Unified Theory of exciplex formation by intermolecular electron transfer or straightforward light excitation of complexes is developed. It includes the reversible dissociation of exciplexes to a singlet ion pair, subjected to spin conversion and recombination to either the ground or triplet state. In the contact approximation the quantum yields of free ions, exciplexes, and triplet products of recombination are calculated analytically. The main results of previous spinless theories are reproduced and shown to be identical to those available with the Integral Encounter Theory.