The problem of spin–orbit coupling (SOC) of exciton bands in molecular crystals is considered. In addition to the usual intramolecular SOC terms, intermolecular SOC terms are obtained if the exciton Bloch functions are properly antisymmetrized and if finite overlap of nearest neighbor molecular functions is accounted for. The magnitude of the intermolecular terms depends on the exciton wave vector k. Numerical calculations on the first triplet exciton bands of 1,2,4,5-tetrachlorobenzene crystals indicate that intermolecular SOC terms are approximately 2×10−3 as large as allowed one-center intramolecular terms. This is comparable in magnitude to vibronically induced SOC which is important in many isolated molecules. The effects of triplet exciton intermolecular SOC on intersystem crossing, radiative relaxation, and nonradiative relaxation are discussed for ππ* triplet exciton bands.