Guest editorial: revised selected papers from the LION 13 conferenceGuest editorial: revised selected papers from the LION 13 conference Εισαγωγή Επιμελητή Editorial 2022-11-032021enIn May 2019, we had the honor of organizing the thirteenth installment of the conference series “Learning and Intelligent Optimization” (LION) in Chania, Crete, Greece. This conference (https://www.lion13.pem.tuc.gr/), which continued the successful series of LION events, was aimed at exploring the intersections and uncharted territories between machine learning, artificial intelligence, mathematical programming and algorithms for hard optimization problems. The conference was very successful in attracting researchers from around the world and in bringing together experts from these areas to discuss new ideas and methods, challenges and opportunities in various application areas, general trends and specific developments. This special issue of the journal of Annals of Mathematics and Artificial Intelligence is devoted to LION 13. The selected papers presented here are full length versions which have undergone a standard refereeing process appropriate for journal papers. The papers accepted fall broadly under the areas of Machine learning, Artificial Intelligence, Swarm Intelligence, Global Optimization, Discrete Optimization, Multiobjective Optimization, Evolutionary Algorithms and Multi-Agent Systems.http://creativecommons.org/licenses/by/4.0/Annals of Mathematics and Artificial Intelligence898–9737–739 Matsatsinis Nikolaos Ματσατσινης Νικολαος Marinaki Magdalini Μαρινακη Μαγδαληνη Marinakis Ioannis Μαρινακης Ιωαννης Pardalos, P. M., 1954-, (Panos M.) Springer Machine learning Artificial Intelligence Swarm Intelligence Global Optimization Discrete Optimization Multiobjective Optimization Evolutionary Algorithms and Multi-Agent Systems