The Dillon, Matheson, and Bradford and the Brown hypotheses for the mechanism of film formation of latexes are extended, two latex particles in a drop of water being given as a model. As the water evaporates, the particles are brought together, so that their stabilizing layers are in contact and their further approach is hindered. The pressure forcing the particles together is increased by the further evaporation of water (that is, by the forces arising from the water air interfacial tension), until the stabilizing layers are ruptured and a polymer polymer contact is formed. Once this occurs, the pressure exerted upon the particles is increased further by the forces arising from the polymer water interfacial tension. Numerical values for the pressure exerted upon the particles are calculated as a function of latex particle size, degree of coalescence, and interfacial tensions both of water against air and polymer against water. Similar calculations with a latex particle coalescing against a flat surface (for example, a substrate) as a model demonstrate the importance of the contact angle between the polymer and the flat surface. The hypotheses developed are used to explain various experimental observations.