Size and dispersity control of metallic nanoparticles is of fundamental necessity for their useful chemical implementation. A single-step synthesis of Au nanoparticles 4-15 nm in diameter and with low polydispersity is presented. Amine-induced reduction of a Au(I) precursor in the presence of coordinating ligands leads to nucleation of small particles which ripen to form larger particles. The rate of particle growth and subsequent aggregation is strongly dependent on the relative concentrations of protecting ligands and is monitored by both transmission electron microscopy and LTV-visible absorption spectroscopy.