Because of the need for thin-film devices in integrated optics, the research of optical films has been greatly expanded in the past few years. We review formation of amorphous optical films by vacuum evaporation, reactive sputtering, solution deposition, and gas-discharge polymerization. We also discuss growth of single-crystal optical films by diffusion, melting, chemical vapor deposition, and liquid phase epitaxy. While most of the films available today are still far from perfect, we hope that this review will stimulate new ideas and new efforts in this important area of research.