This chapter will introduce three new IETF transport layer protocols in support of multimedia data transmission and discuss their usage. First, the stream control transmission protocol (SCTP) will be described; this protocol was originally designed for telephony signaling across the Internet, but it is in fact broadly applicable. Second, UDP-Lite (an even simpler UDP) will be explained; this is an example of a small protocol change that opened a large can of worms. The chapter concludes with an overview of the datagram congestion control protocol (DCCP), a newly devised IETF protocol for the transmission of unreliable (typically real-time multimedia) data streams.