This chapter deals with the application of catalytic systems based on nickel nanoparticles to the hydrogen-transfer reduction of olefins, carbonyl compounds, and the reductive amination of aldehydes. The transfer hydrogenation of alkenes is described with unsupported NiNPs and clay-entrapped NiNPs using 2-propanol and hydrazine as the hydrogen sources, respectively. Carbonyl compounds have been mainly reduced in the presence of 2-propanol and nickel catalysts such as unsupported NiNPs, Ni-coated nano-ferrite, NiNPs embedded on a silica support, Ni@SiO2 yolk–shell nanocatalysts, NiNPs/montmorillonite and NiNPs/aluminosilicate; unsupported NiNPs have also been used in the presence of ammonium formate. The reductive amination of aldehydes by transfer hydrogenation is presented under the catalysis of unsupported NiNPs using 2-propanol as the hydrogen source in the absence of any added base. Therefore, simple and easy-to-prepare NiNPs can be considered a real and cheap alternative to noble-metal based catalysts in hydrogen-transfer reactions. In addition, due to the heterogeneous nature of all the catalytic systems shown herein, they can be easily recovered and reused in several cycles, maintaining high catalytic activities and displaying reactivity superior to that of other nickel catalysts, including Raney nickel.