ITU-T provides several languages for telecommunication applications (see Recommendations in the X.680 series, Z.100 series, Z.120 series, Z.130 series, Z.140 series and Z.150 series). Although each of these languages can be used on its own, they can also be used as a family of system design languages by showing the relationship between the languages. For this purpose, UML defined by the object management group (OMG) can be used as a framework to bind the languages together and capture the relationships through the creation of a UML profile for each language. The purpose of this Recommendation is to provide a guideline on how to read and write such profiles.