Interface effects have been found to play a key role in controlling the epitaxial nature and physical properties on the highly epitaxial ferroelectric thin films. Thin film ferroelectrics are dominantly affected by the strains induced by lattice misfits between the films and the substrates, surface step terrace, both step height and terrace dimension, and the surface terminations. The natures of interface induced local strain formations, edge dislocations, and antiphase domain boundaries are reviewed in this article.