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Distributed energy resources (DER) are in transition from the lab to the marketplace. The defining characteristic of DER is that they are active devices installed at the distribution system level, as opposed to the transmission level. While no specific size range has been defined, most distribution systems would have difficulty accommodating distributed generating resources larger than 10 MW/MVA at any single location and many systems may have even lower limits. Distributed energy resources include generation resources such as fuel cells, micro-turbines, photovoltaics, and hybrid power plants or storage technologies such as batteries, flywheels, ultra capacitors and superconducting magnetic energy storage. They may also consist of dynamic reactive power control devices and possibly customer end-use load controls. This paper summarizes technical requirements for large-scale integration of active devices into the existing distribution infrastructure to maintain or enhance reliability. The paper is intended to lay the groundwork for a multi-year program of research necessary to facilitate the transition to such a system. The scope of the research includes consideration of control systems including the sensors and instruments necessary to gather intelligence for real-time power management and dispatch or coordination among distributed generation resources and with utility distribution systems. It also includes improved modeling techniques to better characterize the technologies and their impacts on the distribution (and ultimately the transmission) system.