This Account describes the development and mechanistic study of the cycloisomerization and cyclization/hydrosilylation of functionalized dienes catalyzed by cationic palladium(II) complexes. These transformations are characterized by good functional group compatibility, high regio- and stereoselectivity, and low air- and moisture-sensitivity. Mechanistic studies of palladium phenanthroline-catalyzed diene cycloisomerization and cyclization/hydrosilylation established mechanisms involving C-C bond formation via intramolecular carbometalation of an alkyl olefin chelate complex, which was directly observed in the context of cyclization/hydrosilylation.