The increasing penetration of intermittent and stochastic distributed energy resources (DERs), including renewable generations, active loads and energy storage, brings great challenges for traditional distribution networks. Active distribution systems (ADS) have coordinated controls and active managements in place and make the higher penetration and integration of distributed energy resources possible. This special issue is dedicated to reflecting the latest progress and technologies in ADS. There are 17 papers included focusing on the following 7 topics: 1) Planning; 2) Control and protection; 3) Management; 4) System analysis and market; 5) Energy storage; 6) Power quality; 7) Communication. In summary, these 17 papers are well organized to address various challenging issues in ADS. It is hoped that this issue will serve as an introduction for future research aimed at the interconnection of DERs to distribution network.