AbstractSome fundamental aspects of carbocation chemistry are discussed in their relationship to our better understanding of carbocationic olefin polymerization and alkane condensation reactions including those of methane. Whereas trivalent alkyl cations, i.e. R3C+play the key role in the former, the latter is made possible through the intermediacy of five coordinate carbocations of the CH5+type. In conventional acid catalyzed reactions carbocations are always in equilibrium with their corresponding olefins, whereas under superacidic, stable ion conditions carbocations can be generated and reacted free of such equilibria. The chemical consequences of these differences are discussed in polymerization, as well as in alkylative or oxidative alkane condensation reactions.