The search for radical initiators able to work under soft conditions is a great challenge, driven by the fact that the use of safe and cheap light sources is very attractive. In the present paper, a review of some recently reported photoinitiating systems for polymerization under soft conditions is provided. Different approaches based on multi-component systems (e.g., photoredox catalysis) or light harvesting photoinitiators are described and discussed. The chemical mechanisms associated with the production of free radicals usable as initiating species or mediators of cations are reported.
