Transmitted-light methods reveal more details of the morphology of fiber-reinforced polymeric composites than are observable using any other available microscopy techniques. This chapter describes the various aspects relating to the selection and preparation of ultrathin-section specimens of fiber-reinforced polymeric composites for examination by transmitted-light microscopy techniques. The preparation steps covered are a selection of the rough section, preparation of the rough section for preliminary mounting, grinding and polishing the primary-mount first surface, mounting the first surface on a glass slide, and preparing the second surface (top surface). The optimization of microscope conditions and analysis of specimens by microscopy techniques...