This review concentrates on the recent acpects in the sensitized (indirect) decomposition of cationic photoinitiators, namely onium salts. There are three general methods where various additives play an indirect role to decompose onium salts. The first method involves electron transfer reaction of electronically excited sensitizers with onium salts to yield sensitizer radical cations. In the second method electron donor compounds in charge transfer complexes undergo similar electron transfer reactions. In this case the radical cations of the electron donor compounds are formed. Finally, photochemically formed radicals can induce the initiation of cationic polymerization via electron transfer or addition-fragmentation mechanisms.