In recent years, the polymer field has been revolutionised by the development of techniques for controlling the molecular weight and architecture of the polymer produced in free-radical polymerisation. We have been using quantum chemistry to study the mechanism and kinetics of these techniques with a view to designing improved control agents for ‘difficult’ monomers, such as ethylene. Our early studies focused on the Australian-invented RAFT process, and this work culminated in the development and patenting of the first multipurpose RAFT agent, capable of controlling monomers with disparate reactivities. Our studies of the intermediate radical in the process, also led to the discovery (in collaboration with Professor Barner-Kowollik, UNSW) of a new method for controlling free-radical polymerisation using thioketone spin traps. We are now working with the inventor of Atom Transfer Radical Polymerisation (ATRP), Professor Matyjaszewski (Carnegie Mellon), to study the mechanism of ATRP with a view to improved catalyst selection and design. Recently, we highlighted the important role of penultimate unit effects on the initiation step of this process and demonstrated that, for the alkyl halides relevant to ATRP, outer-sphere electron transfer occurs preferentially via dissociative electron transfer.