ess is known as source coding, and may apply to analogue information such as voice, audio and video, or may apply to discrete data streams such as text or numbers. The source coding process, which is the focus of this chapter, coverts an ana- logue signal to an equivalent digital signal. In many cases it also removes redundancies and produces a data stream with a size close to the source entropy as may be perceived by a human recipient. A number of source coding techniques exist, classified by their efficiency vis-à-vis the information source entropy. Because telecommunications equipment needs to inter-operate, the choice of a source coding technique is usually determined by an international standard. The standards decisions are generally based on the technical performance of the source coding technique as well as business issues such as equipment complexity and backward compatibility. Intellectual property rights, patent restrictions and such are also important considerations. There may also exist policy considerations: development of international Message Message source encoder transmitter Transmission infrastructure/ channel Message Message decoder receiver Figure 5.2 Telecommunications block diagram From Analogue to Digital standards requires collaboration from national standardisation bodies. Generally the market for most, if not all, telecommunications products is global, and therefore many national agencies need to take part and approve such standards. This chapter discusses how continuous analogue information may be represented in a discrete digital form, and how such representation may be done with a minimal number of bits. We show that the mechanisms for representing such signals follow principles developed by Shannon as described in Chapter 4. Popular source coding techniques for data, voice, audio, image and video signals are described. We demonstrate how these techniques are used in popular information storage and communications applications such as zip programs, voice over internet protocol (VoIP), 