The IV International Congress of Trail Running, organized by the Servei d'Esports of the Universitat Jaume I and the 5th International Congress of Medicine & Science in ultraendurance sports organized by the Ultra Sports Science Foundation in collaboration with the Club de Carreres de Muntanya Desert Amunt and Penyagolosa Trails, will be held on 9 and 10 May 2018 at the Universitat Jaume I of Castellón de la Plana, Spain. This event will be the scientific precursor of the World Trail Championship, which will take place in the province of Castellón. This event has the institutional support of the Diputación Provincial de Castellón (Castellón Council) and the city of Castellón, as well as the sponsorship of the Cátedra Endavant Villarreal CF de l’Esport.