Abstract: Ferroelectrics possess spontaneous polarization which can be switched by applying an electric field; this property can be used to produce random access memories. Some ferroelectrics have large nonlinear optical coefficients and strong electro－optical effects, which may be exploited in opto－electronic and optical communication devices. In this work ferroelectric Bi4-xLaxTi3O12, SrBi2Ta2O9, PbZrxTi1-xO3 and LiNbO3( films of the perovskite structure as well as related perovskite La(Sr,Co)O3 and LaNiO3 electrode films were studied, and the interaction between defect charges and domain walls and their dynamic behavior in an ac electric field investigated to elucidate the mechanism of the fatigue phenomenon. Studies on the lattice structures and defects of the films by high resolution transmission electron microscopy and Raman scattering measurements were made to find a way to optimize the electrical properties. The microstructure and properties of film/electrode interfaces were also studied, from which the optimal film/electrode combinations for memory applications were proposed. The growth mechanism of ferroelectric thin films in an electric field was investigated both experimentally and theoretically, and a technique to control the growth texture by using an electrical field was developed.