The purpose of recommending MSC (message sequence chart) is to provide a trace language for the specification and description of the communication behaviour of system components and their environment by means of message interchange. Since in MSCs the communication behaviour is presented in a very intuitive and transparent manner, particularly in the graphical representation, the MSC language is easy to learn, use and interpret. In connection with other languages it can be used to support methodologies for system specification, design, simulation, testing, and documentation. This Recommendation is revised to reflect the experience and changes in use of the language since the last major revision of the language (to MSC-2000) in 1999 and the last update in 2004.