Dear Colleagues, Due to numerous requests the deadline for submissions for the ECCO XXXIX - CO 2026 joint Conference on Combinatorial Optimization is extended to NEW Abstract submission deadline: March 28 , 2026 The CO XXXIX - CO 2026 joint Conference will take place on May 14-16, 2026 in Lisbon, Portugal. ECCO (the European Chapter on Combinatorial Optimization<https://en.wikipedia.org/wiki/European_Chapter_on_Combinatorial_Optimization>) is a Working Group of EURO (the Association of European Operational Research Societies<https://www.euro-online.org/web/pages/1/home>) that provides an excellent opportunity to discuss recent and important issues in Combinatorial Optimization and its applications. CO series of biennial symposia, the Combinatorial Optimization Conferences, started in the UK in 1977 with meeting venues alternated between the UK and continental Europe. Keynote speakers: William Cook, University of Waterloo Gabor Galambos, University of Szeged Joerg Kalcsics, University of Edinburgh Sergio Garcia Quiles, University of Edinburgh We invite researchers interested in the following areas to submit an abstract: * theory and applications of combinatorial optimization; * optimal solution methods, approximation algorithms and heuristics for combinatorial optimization problems; * integer programming, global optimization, stochastic integer programming, multi-objective programming, graph theory and network flows; * application domains include, but are not limited to: logistics and supply chain optimization, manufacturing, energy production and distribution, land consolidation, telecommunications, bioinformatics, finance. More details can be found at https://ecco2026.campus.ciencias.ulisboa.pt/ The Program Committee Chair Luis Gouveia