A Jewish communist, Diamant was a committed member of the underground resistance during World War II. On more than one occasion he was offered safe passage to England but chose instead to remain in France. After the war he worked initially with the UJRE (l'Union des Juifs pour la Résistance et l'Entraide) and devoted himself to documenting the Jewish resistance by collecting original documents and writing and publishing extensively on the subject. Jewish Underground Resistance includes a wide range of materials: Documents in Yiddish: Leaflets and Internal Documents Documents of Jewish Resistance Groups and other Groups; Miscellaneous or Unidentified Groups during the Occupation; Miscelleaneous or Unidentified Groups after the Occupation; Documents Relating to Collaboration Documents on Prisons, Prisoners and Deportées; French Leaflefts: Jews and Jewish Underground Groups; Incomplete and Unidentified Documents.