The copper-catalyzed selective mono-N-alkylation of primary amides or arylamines using alkylsilyl peroxides as novel alkylating agents is reported. The reaction proceeds under mild reaction conditions and exhibits a broad substrate scope with respect to the alkylsilyl peroxides as well as to the primary amides and arylamines. Mechanistic studies suggest that the present reaction should proceed through a free-radical process including alkyl radicals generated from the alkylsilyl peroxides.