The consecutive two reviews summarize novel metal-free living cationic polymerizations that proceed via degenerative chain-transfer mechanism through reversible activation of dormant carbon-sulfur bonds of thioesters and thioether compounds. This first review is directed to the reversible addition fragmentation chain-transfer (RAFT) cationic polymerization via reversible activation of the dormant thioester bonds by the cationic propagating species generated from a small amount of triflic acid as the cationogen. The obtained polymers possess controlled molecular weight up to 1 ×10⁵, narrow molecular weight distributions (M_w/M_n < 1.1), and controlled chain-end groups in cationic polymerization of not only vinyl ethers and p-alkoxystyrene but also even p-hydroxystyrene (p-vinylphenol) without protection of the phenolic functions. The thioester-chain end can be converted into radical RAFT polymerization to enable the synthesis of block copolymers between cationically and radically polymerizable monomers, such as vinyl ether and vinyl acetate or acrylate.