The Dortan massacre was a massacre in which approximately 35 French civilians  were killed by Wehrmacht volunteers in the village of Dortan, Ain during World War II. It was perpetrated by Volunteer Cossack-Stamm-Regiment 5, part of the Freiwilligen-Stamm-Division, in 12–21 July 1944 during Operation Treffenfeld. It was part of a wider German anti-partisan offensive against the French Maquis de l'Ain et du Haut-Jura, which staged a massive uprising in mid-1944 along with other French resistance groups.