This chapter outlines the recent advances in living cationic polymerization and the precise synthesis of sequence-controlled polymers in this field. Living cationic polymerization has emerged as a tool for the precise synthesis of functional polymers with well-defined structures, such as functional polymers with narrow molecular weight distributions (MWDs), various block copolymers, and star-shaped polymers. By using the continuous living cationic polymerization system, various thermosensitive diblock copolymers are synthesized with designed MWDs. Based on the recent research in this active area, the chapter describes various alternating polymers prepared via controlled cationic polymerization and sequence control based on the cationic copolymerization of vinyl and cyclic monomers. Various cationic polymerizations performed using the flow microreactor systems proceeded in a living manner to produce polymers with narrow MWDs or block copolymers. Various types of block copolymers have been obtained via two consecutive living polymerizations, mainly those from cationic to radical.