The generation of asymmetry in a chiral crystal environment is very interesting in view point of the origin of life as well as organic syntheses. Two subjects are discussed; one is the asymmetric photoisomerization in chiral crystalline field and the other is a racemic-to-chiral transformation in a racemic crystal on exposure to visible light. Since the reactions proceed with retention of the single crystal form, the processes can be easily observed by X-ray analysis and the mechanism is explained on the basis of the reaction cavity which represents the void space around the reactive group in the crystal structure.
