The spontaneous formation of lipid vesicles (liposomes) in aqueous lecithin/bile salt mixtures is studied using time-resolved static and dynamic light scattering. These measurements reveal a strong dependence of the kinetic rates and end-state liposome properties on total amphiphile concentration and, even more pronounced, on ionic strength. The observed trends contradict equilibrium calculations, but are in quantitative agreement with a kinetic model that we present. This model identifies the key kinetic steps during vesicle formation: rapid formation of disc-like intermediate micelles, growth of these micelles and closure to form vesicles. This work offers conclusive evidence for kinetic rather than thermodynamic control of the end-state properties.