Studies on volumetric three-dimensional (3-D) displays are reviewed briefly. A volumetric display method based on 3-D scanning of an inclined image, developed by the author, is introduced. An optical image of a two-dimensional (2-D) display placed obliquely in an optical imaging system is moved laterally by a mirror scanner. Inclined cross-sectional images of a 3-D object are displayed on the 2-D display in accordance with the position of the image plane to form a volumetric image. The three-dimensional images formed by this display system satisfy all the requirements for stereoscopic vision. Experimental results of 3-D imaging achieved by a volumetric display system using a digital micromirror device are presented. Research for improving the practical performance of the volumetric display, such as realizing real-time volumetric imaging from 3-D measurement data and forming volumetric directional images and 3-D fluorescent images, is presented.