The Object Management Group is extending the widely-used Unified Modeling Language (UML) standard by defining a standard “profile” for real-time systems development. This profile includes specific capabilities for representing various models of time, different models of concurrency, and system resources in general (e.g., physical and logical devices, semaphores, task control blocks). A fundamental feature of the profile is the ability to attach quantitative information to UML models. This enables the construction of models that can be used to predict key real-time characteristics, such as response times or memory requirements, early in the development process. This paper describes the major features of this emerging standard.