Metallic nanoparticles and processes for forming metallic nanoparticles. In one aspect, the invention is to a process for forming nanoparticles comprising the step of heating a solution comprising a first metal precursor and a nucleating agent (e.g., nucleate nanoparticles or a nucleate precursor) in the presence of a base under conditions effective to form the nanoparticles. The first metal precursor preferably comprises a cationic metal species having a low reduction potential. The invention is also to a nanoparticle or plurality of nanoparticles, each nanoparticle comprising a core having a largest dimension less than about 10 nm; and a metal layer substantially surrounding the core and having a largest dimension less than about 200 nm.