Domain-specific languages (DSLs) provide developers with the ability to describe applications using language elements that directly represent concepts in the application problem domains. Unlike general-purpose languages, domain concepts are embedded in the semantics of a DSL. In this chapter, the authors present an interpreted domain-specific modeling language (i-DSML) whose models are used to specify user-defined communication services, and support the users’ changing communication needs at runtime. These model changes are interpreted at runtime to produce events that are handled by the labeled transition system semantics of the i-DSML. Specifically, model changes are used to produce scripts that change the underlying communication structure. The script-producing process is called synthesis. The authors describe the semantics of the i-DSML called the Communication Modeling Language (CML) and its use in the runtime synthesis process, and briefly describe how the synthesis process is implemented in the Communication Virtual Machine (CVM), the execution engine for CML models.