TRANSFORMATION of the existing electric power systems into modern smart grids is gaining momentum as mostjur-risdictions are seeking ways to lower their energy consump-tions, life cycle costs and greenhouse gas(GHG) emissions. The transformation requires the integration of significant renewable energy into the existing power systems, which has posed tremendous technical and operational challenges involving the issues of voltage and frequency stability, insuf-ficient energy storage, resources for system balancing and dispatch, renewable energy intermittency, and much more. During a recent research trip of mine to an island country, I got the first-hand experience in how the fast down-ramping events of a large central photovoltaic(PV) plant could cause load shedding and PV generation curtailment. Innovative solu-tions are needed to support this power system transformation, as the need for additional system resources can no longer be met by building more central generation plants. As an integral part of modern power systems, distributed energy resources(DER) have been rapidly deployed through-out the world, initially as an effective means of clean gener-ation to displace fossil fuels and subsequently as resources to provide power system functions such as ancillary services and peak load reduction. DERs include distributed generation systems such as wind, solar and CHP systems, energy storage units including electric vehicles, controllable loads, and as-sociated power conversion and control systems, all in power distribution networks. The innovative solutions to facilitate the seamless integration of DERs into electric grids and the creation of new power systems resources have never been more important than today. These solutions are critical to enabling max-imum penetration of renewable energy, while allowing utilities to maintain hi g h standards of g rid stabilit y , reliabilit y , flexibilit y , and economy. The purpose of this Special Issue is to review the state-of-the-arts in the DER fields and to disseminate the recent technological advancement in DERs, pertinent to analysis, de-sign, conversion, control, performance, and application.