Triplet‐sensitized irradiation of either Vitamin D or transVitamin D establishes a photo‐equilibrium between the two isomers, the position of which varies with the triplet energy of the sensitizer. In the presence of oxygen, selective photooxygenation of trans‐Vitamin D takes place. The applicability of sensitization for the preparation of cis‐ and trans‐Vitamin D and derivatives thereof is shown.