We are interested in utilizing principles of supramolecular chemistry and molecular recognition to direct chemical reactivity in the organic solid state. The ability to control reactivity in the solid state has implications for organic synthesis (e.g. green chemistry) and materials science (e.g. solid-state devices). In this poster, we will describe the ability of 1,8-naphthalenedicarboxylic acid (1,8-nap) to assemble trans-1-(methyl)-2-(4-pyridyl)ethylene (mvp) within a three-component molecular assembly, (1,8-nap)•2(mvp), held together by two OH•••N hydrogen bonds. Single-crystal X-ray diffraction reveals that the olefins of the assembly lie in a position suitable for a regiocontrolled intermolecular [2+2] photodimerization in accordance with Schmidt's postulate. We will demonstrate that ultraviolet radiation of the solid results in a stereospecific [2+2] photodimerization in quantitative yield. This study suggests that alkyl groups may be attached directly to olefins for reaction in organic solids.