The authors discuss digital optics, a technology for processing, transport, and storage of optical digital information. Digital optics offers both the high temporal bandwidth of fiber communications and the high connectivity and information density of optical imaging. The energy dissipation per bit of communicated information, as well as the chip area dedicated to interconnections, can be significantly lower in optics than in high-speed electronics. This motivates the introduction of parallel optical interconnections through free space in communication-intensive areas of digital information processing such as switching in telecommunications and within multiprocessors. Digital optical circuits can be constructed by cascading two-dimensional planar arrays of optical logic gates interconnected in free space. The state of the art and the trends in digital optical information processing systems for optical logic, optoelectronic interfaces, and optical free-space interconnection systems are reviewed.>