A codec is the mechanism by which video and audio signals are compressed to conserve bandwidth before transmission across a telecommunication network. It may be implemented either in hardware or software. In the past, manufacturers sometimes used proprietary codecs that were incompatible with those from other manufacturers. As network usage became more widespread, however, it became clear that standards were needed to permit interoperability between equipment from different manufacturers. Regardless of the coding standards employed, the primary concerns for the user of a codec system are the quality of the audio and video transmitted. How does one decide what kind of codec to use? For telehealth applications, good quality is important, so it is best to look at products from established manufacturers. Ultimately, the choice of a codec for telehealth depends primarily on the trade-offs between quality, cost, bandwidth requirements and interoperability required by the application(s) for the system, and the environment in which it will be used.