Reversible addition fragmentation chain transfer (RAFT) polymerization is one of the most extensively studied reversible deactivation radical polymerization methods for the production end-group can easily be of well-defined polymers. After polymerization, the RAFT agent converted into a thiol, opening manifold opportunities for thiol modification reactions. This review is focused both on the introduction of functional end-groups using well-established methods, such as thiol-ene chemistry, as well as on creating bio-cleavable disulfide linkages via disulfide exchange reactions. We demonstrate that thiol modification is a highly attractive and efficient chemistry for modifying RAFT polymers.