In this Account, we describe our recent research progress in the development of the functionalization of unsaturated substrates catalyzed by low-valent nickel. In particular, we discuss nickel-catalyzedazide-alkyne cycloaddition (NiAAC), [2 + 2 + 2] cycloaddition of diynesand nitriles, hydrosilylation of alkynes, and dicarbo functionalization of1,3-enynes. Moreover, we highlight our mechanistic studies aimed at elucidating catalytically active nickel intermediates, thereby contributing to the understanding and expansion of nickel-catalyzed synthetic methodologies.