Abstract
We calculate the coercive field of thin ferroelectric films caused by the domain wall pinning by surface inhomogeneities. The Joanny-De Gennes formula is generalized to the elastic energy of the line of intersection of the domain wall with the surface of ferroelectrics. The coercive field induced by the pinning is shown to be inversely related to the film thickness and to have a magnitude of the order of that observed in experiments.