The Usumacinta River (; named after the Howler monkey) is a river in southeastern Mexico and northwestern Guatemala. It is formed by the junction of the Pasión River, which arises in the Sierra de Santa Cruz (in Guatemala) and the Salinas River, also known as the Chixoy, or the Negro, which descends from the Sierra Madre de Guatemala. It defines part of the border between Guatemala and the  Mexican state of Chiapas, then continues its northwesterly course, meandering through the Mexican state of Tabasco to the Gulf of Mexico.