The kinetics of two-dimensional phase transitions of sulfide, iodide, bromide, and chloride ions on Ag(111) was investigated at anionic concentrations ranging from 1 x 10(-4) to 1 x 10(-3) M by measuring the time dependence of the charge following steps from a potential negative enough to exclude anionic adsorption to a potential in the range of stability of either the first or the second, more compressed, ordered overlayer of the anions. The kinetic behavior is interpreted by a model that accounts for diffusion-controlled random adsorption of the anions, followed by progressive polynucleation and growth. When stepping to the potential range of stability of the second overlayer, the kinetic behavior is accounted for by assuming that the passage from total desorption to the second overlayer occurs via the intermediate formation of the first one.