The Moving Pictures Expert Group (MPEG) was started in 1988 as a working group within ISO/IEC with the aim of defining standards for digital compression of audio-visual signals. The MPEG's first aim was to define a video coding algorithm for application on digital storage media, in particular for CD-ROM. Very rapidly the need for audio coding was added and the scope was extended from being targetted solely on CD-ROM to trying to define a generic algorithm capable of being used by virtually all applications, from storage-based multimedia systems, television broadcasting, and communications applications such as video-on-demand to face-to-face communication. The MPEG's first project, MPEG-1, was published in 1993 as ISO/IEC 11172. It is a three part standard defining audio and video compression coding methods and a multiplexing system for interleaving audio and video data so that it can be played back in close synchronisation. During 1990, the MPEG recognized the need for a second, related standard for coding video at higher data rates in an interlaced format (the essential technical difference is that MPEG-1 is designed for coding progressive pictures whereas MPEG-2 is optimised for interlaced pictures, MPEG-1 bit-streams are decodable on MPEG-2 decoders). The MPEG-2 standard is capable of coding standard definition television at bit-rates from about 4-9 Mbit/s and high definition television at 15-25 Mbit/s. For interlaced video signals coded at bit rates above about 3 Mbit/s, MPEG-2 is more efficient than MPEG-1. MPEG-2 audio is backwards compatible with MPEG-1 audio and extends the system to multi-channel surround sound coding. (5 pages)