One of the most important considerations for the current VLSI/SOC design is power, which can be classified into power analysis and optimization. In this survey, the main concepts of power optimization including the sources and policies are introduced. Among the various approaches, dynamic power management (DPM), which implies to change devices states when they are not working at the highest speed or at their full capacity, is the most efficient one. Our explanations accompanying the figures specify the abstract concepts of DPM. This paper briefly surveys both heuristic and stochastic policies and discusses their advantages and disadvantages.