The collection “On the Internal Front of the Civil War” includes documents and testimony about the explosion of the Moscow Committee of the RCP (b) by “underground anarchists” in Leontyevsky Lane on September 25, 1919, about security operations against anarchists, maximalist Socialist-Revolutionaries and left Socialist-Revolutionaries, suppression peasant uprisings and the Makhnovist movement. Among them are the memoirs of the Menshevik A. Ioffe about his meeting and conversations with Fanny Kaplan on the eve of the assassination attempt on V.I. Lenin, a unique interrogation of one of the Socialist Revolutionary workers, Kaplan’s henchmen, documents about the secret Chekist operation “Lead” in Kazan, the anarchists’ occupation of Voronezh and their disarmament, materials about “showdowns” between field commanders in the Red camp and inside the White camp. Many archival documents were previously unknown and are being published for the first time. The documents as a whole do not reflect the open confrontation between whites and reds on the fronts of the Civil War, which is in the focus of public attention, but little-known or “behind the scenes” facts, without which the true history of the events of the century the limitation period is not complete.