Optical and spectroscopic properties of Langmuir-Blodgett (LB) monolayers and multilayers are being measured to characterize the films, to understand their two-dimensional behavior and to follow chemical and physical changes. Orientation of groups and molecular packing have been analyzed by Fourier transform IR spectroscopy at glancing angle, from waveguide Raman scattering and from near- edge X-ray fine structure. Use in electronic and optical devices has excited many, especially with non-linear phenomena needed to control or modify light optically for communication and storage. Recent optical results on thin monolayer and multilayer assemblies will be reviewed, including both the linear and non-linear aspects. Effects and phenomena will be illustrated with examples to give an appreciation for their use and to display some of our new knowledge about LB films. © 1988.