An overview of the miniaturization technologies and their application to energy systems is presented. Based on the technologies referred to as MEMS (microelectromechanical systems) or MST (micro systems technologies), silicon based micromachining, deep X-ray lithography and the micro mechanical machining processes (micro drilling, milling, cutting, electrical discharge machining, laser, focused ion beams, etc.) will be discussed in the context of application to fluid flow, heat transfer, fluidics and energy systems. An overview of fundamental research and applications will be made with emphasis on the work in the United States. The collaborative work in progress by the Institute for Micromanufacturing and the Pacific Northwest National Laboratories is highlighted. In particular, the on-going development of a micro HVAC (heating, ventilating and air conditioning) system is given specific attention. Devices and/or systems such as micro heat pumps, heat pipes, evaporators, condensers, heat exchangers, compressors and the like will be presented. Advantages, disadvantages and the rationale for miniaturization will be discussed. Current needs and markets will be discussed along with a discussion for future needs.