This article reviews recent approaches toward the synthesis of exo-olefin terminated polyisobutylene (PIB) or so-called highly reactive PIB (HR PIB). The advantages and disadvantages of methods based either on living cationic polymerization or using complexes of Lewis acids with ethers are discussed here from the point of view of their industrial relevance. The first method is unique in terms of the synthesis of well-defined di- or trifunctional exo-olefin terminated polyisobutylenes. The second one could be an alternative route towards HR PIB, which is currently obtained at the industrial scale via BF₃-coinitiated polymerization of isobutylene. Special focus is laid on the recent progress in the cationic polymerization of 1,3-dienes (isoprene, 1,3-pentadiene) allowing us to synthesize well-defined low molecular weight poly(1,3-diene)s with a high degree of unsaturation of the polymer chain (>85%). This review article shows that the Lewis acid-co-initiated cationic polymerization of isobutylene and 1,3-dienes has still not been fully explored, and new innovative initiating systems of high commercial interest can be discovered.