Silver nanoparticles were synthesized by an inert gas condensation method using flowing helium in the process chamber. Nucleation, growth mechanism, and the kinetics of nanoparticle formation in vapor phase are studied. Effect of process parameters, such as evaporation temperature and inert gas pressure, on the particle crystallinity, morphology, and size distribution are examined. Particles were synthesized at evaporation temperatures of 1123, 1273, and 1423 K and at helium pressures of 0.5, 1, 5, 50, and 100 Torr. Synthesized silver nanoparticles were characterized by x-ray diffraction (XRD) and transmission electron microscopy (TEM). The particle size ranged from 9 to 32 nm, depending on the growth conditions. At lower evaporation temperature and inert gas pressure, smaller particles with spherical shape showing less agglomeration are formed. Based on the experimental results and theoretical model of surface free energy and undercooling as a function of evaporation temperature and inert gas pressure, particle formation is analyzed. A simple operating map for nanoparticle synthesis is presented. The theoretical model is well supported by the experimental data.