The use of dormant species has opened a new era in precision polymerization and has changed the concept of living polymerization. The dormant species can be exchanged into the active species via reversible termination or via reversible chain transfer. Professor Mitsuo Sawamoto has greatly contributed to the establishment of the concepts of living cationic and radical polymerizations based on the reversible activation of dormant species. This highlight, dedicated to Professor Sawamoto on his retirement from Kyoto University, provides an overview of reversible or degenerative chain-transfer (DT) processes, which are effective in controlling all chain-growth polymerizations, including radical, cationic, anionic, coordination, ring-opening metathesis, and ring-opening polymerizations. In addition, structures with novel sequences accessible only by a combination of different propagating species with a common DT agent are reviewed. (c) 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 243-254