A radiation curable composition comprising a curable compound, a photo-initiator and a co-initiator, characterized in that said co-initiator is a oligomer or polymer having a repeating unit, said repeating unit comprising at least two tertiary amines, and said polymer being prepared by the polycondensation of di- or oligofunctional Michael acceptors with mono- or oligofunctional aliphatic primary amines or with di- or oligofunctional aliphatic secondary amines or with a mixture thereof.