A comparison of the film forming ability of methyl methacrylate (MMA)/butyl acrylate (BA) latex copolymers stabilised by either a reactive or a non-reactive steric stabiliser is reported and indicates the key role of the degree of polymerisation of the hydrophilic ethylene oxide chain on the coalescence process. The study uses dielectric measurements to follow and identify the various stages of film formation. The ability of the stabiliser to segregate and diffuse from the interfacial layer into the surrounding media influences in both the rate of the coalescence process and the final physical properties of the films formed. Dielectric relaxation and electrical conductivity measurements indicate the mechanistic complexity of the coalescence process and illustrate that the clear differences exist between the behaviour of the two systems investigated. A model for the film formation processes is presented which incorporates the various features identified by the dielectric study.