Novel perspectives in the development of metal complex based photocatalysts operating through an oxidation or a reduction cycle are investigated. Several systems (Fe, Ni, Co, Al, Ru, Ir organometallic complexes) working under soft irradiation conditions are presented. Their photochemistry is studied by steady state photolysis and ESR experiments to define the key points responsible for a high reactivity. Some of them are tested as photoinitiator catalysts in multi-component combinations usable in photopolymerization reactions.