Transmission over real-world networks will occasionally suffer from transmission errors, which can significantly deteriorate the perceived quality of a speech codec. This chapter addresses the problem of transmission errors in packet based voice applications, such as voice over Internet protocol (VoIP). A broad range of techniques for recovery from packet loss on the channel are presented, from channel coding to techniques using speech signal processing methods, as well as both sender-driven and receiver-based methods. The sender based methods include for example retransmission, interleaving and forward error correction (both media-specific as well as media-independent), whereas receiver-based techniques include noise substitution, repetition and synchronisation methods.