Nanoparticle compositions of noble metals, and methods of making them, are described. The nanoparticle compositions are made by reacting a salt or complex of a noble metal, such as Au, Ag, Cu or Pt, with a weak ligand, and a reducing agent, in a single liquid phase. The noble metal is typically provided as a halide or carboxylate. The ligand is preferably a fatty acid or aliphatic amine. The reducing agent is preferably a borohydride reagent, hydrazine, or a mixture thereof. Nanocrystals in the size range of 1 nm to 20 nm are produced, and can be made in substantially monodisperse form.