reversible addition frag mentation chain transfer (RAFT) or catalytic chain transfer (CCT) reactions. All of these variants of controlled radical polymerisation lead to well defined archi tectures with the particular advantage that a much larger number of monomers are suitable and the reaction conditions are much less demanding than those of living ionic polymerisation reactions. Although in controlled radical polymerisation, termination reactions cannot be excluded completely, they are limited in their extent and consequently the mol ecular weight is controlled, the polydispersity index is small and functionalities can be attached to the macromolecules. These features are indicative of the real isation of well defined polymer architectures such as block copolymers, star shaped and comb shaped copolymers.