This paper provides an introduction into the basics of echo cancellation. The paper is kept general but it emphasizes on the emerging Voice over IP (VoIP) market. However, most aspects can also applied to Asynchronous Transfer Mode (ATM) or wireless networks. This paper shows why and where echo cancellation is required, what echo is, and what causes it. It also gives an overview of the standards involved in echo cancellation. The SIDECTM, Infineon’s digital echo canceller, meets the requirements of the VoIP market. This paper shows how it can be integrated into a VoIP system and the advantages the solution offers.