Traditional real-time systems require a priori knowledge of process period and worst-case execution times in order to guarantee application and system performance. Traditional static worst-case execution time analysis has been developed to support this requirement. However, real-time systems have grown beyond static applications developed for unchanging and well-documented hardware and software architectures. They now include (perhaps predominately) a large variety of highly dynamic applications, written by a large number of developers inexperienced with traditional real-time design, and executed on widely varying hardware and software platforms in competition with greedy best-effort applications with unknown processing characteristics. In such an environment, static timing analysis or specification is useless. This sea change in application and system characteristics requires a corresponding change in the tools and techniques used to characterize the application requirements and to meet those requirements. In many instances, dynamic analysis is the only possibly solution.