Abstract: An introduction to spatial sound in the context of hypermedia, interactive multimedia, and virtual reality is presented. Basic principals of relevant physics and psychophysics are reviewed (ITDs: interaural time differences, IIDs: interaural intensity differences, and frequency-dependent attenuation capturable by transfer functions). Modeling of sources and sinks (listeners) elaborates such models to include such as intensity, radiation, distance attenuation & filtering, and reflections & reverberation. Display systems---headphones and headsets, loudspeakers, nearphones, stereo, home theater and other surround systems, discrete speaker systems, speaker arrays, WFS (wave field synthesis), and spatially immersive displays---are described. Distributed applications are surveyed, including stereotelephony, chat-spaces, and massively multiplayer online role-playing games (MMORPGs), with references to immersive virtual environments.