Session Description Protocol (SDP) is used as the mechanism for negotiations of functional, performance, and security parameters of audio, video, and/or data used in multimedia conferencing created by any call control protocol for setting up a session between end users. In order to understand SDP, we need to have a preliminary idea of how it is used in setting up sessions by the call control protocols. Session Initiation Protocol (SIP) is a well-established standardized call control protocol for multimedia conferencing. Recently, the emerging web real-time communication (WebRTC) protocol has also chosen SDP for multimedia session negotiations. The SIP that carries SDP in the message-body of signaling messages for session negotiations between communicating parties is described briefly in this chapter. In addition, the emerging WebRTC that also carries SDP for multimedia session negotiations between browsers is introduced. Both call control protocols have embedded networking capabilities and set up multimedia one-to-one, many-to-many, many-to-one, and one-to-many sessions in communicating environments. Basic information for these call control protocols is provided to show how SDP is used for complicated multimedia session negotiations.