At the beginning of the chapter, some general features are mentioned, including the mechanism of the photocyclization, reaction conditions, attempts at asymmetric photosynthesis, and the synthetic approach to starting materials. The appropriate helical structures and their preparations are described in sections on carbo-, aza-, thia-, and phosphahelicenes and other helicenes. Helicene-like molecules, including dihydrohelicenes, are discussed separately, as well as photochemical transformations of helicenes