This Journal of Decision Systems (JDS) Special Issue on ‘Knowledge-Based Decision Systems’ (KBDS) includes selected and extended papers from two major events organised by the Euro Working Group on Decision Support Systems (EWG-DSS) in 2013, complemented by open call submissions. The two events were: EWG-DSS 2013 Annual Workshop held in Thessaloniki, Greece, from 29 to 31 May 2013, and EURO XXVI-INFORMS Joint International Conference – DSS Stream (with seven sessions) held in Rome, Italy, from 1 to 4 July 2013. From the two events, over 60 papers were presented and assessed by a group of eight experts including members of the EWG-DSS Co-ordination Board. Nine papers ranked as highest quality by the selection committee were selected and the authors were invited to extend their papers and submit them to the JDS Special Issue for consideration. In the meantime, a Call for Papers was placed on the JDS website which attracted another seven submissions. The combined sixteen papers were then put through a rigorous review process. In the end, eight papers received the best evaluation results from the reviewers and were recommended for publication in this Special Issue.