This paper describes the latest developments in the photoinitiating systems, based on onium salts, for cationic polymerization. The goal is, furthermore, to show differences as well as parallels between systems for different modes of photoinitiation. Besides their direct activation upon photolysis at appropriate wavelengths, these salts can undergo indirect decomposition to generate reactive cations. The indirect action can be based on electron transfer reactions between onium salt and photochemically generated electron donor radicals, photoexcited sensitizers and electron reach compounds in the photoexcited charge transfer complexes. Photoinitiation with allylic salts in conjunction with free radical sources is also discussed.