It is obvious that energy-aware scheduling problems largely depend on the tasks and platform under consideration. This chapter provides the system models that we consider in this book. Task models are presented in Sect. 2.1, which includes four types of tasks, namely, frame-based tasks, tasks with precedence constraints, periodic tasks, and sporadic tasks. Uniprocessor power consumption models are provided in Sect. 2.2. Multiprocessor platform models are presented in Sect. 2.3. Section 2.4 discusses other concepts and assumptions related to energy-aware scheduling on multiprocessor platforms. These concepts and assumptions are also important for energy-aware scheduling problems.