Azzo X d'Este (1344–1415) was an Italian condottiero, a member of the House of Este. Born into a cadet branch of the family, he contested the seigniory of Ferrara to the young Niccolò III, an illegitimate son of marquess Alberto d'Este who was under the protection of Pope Benedict IX and Venice. After a failed attempt to poison him, Azzo created a compagnia of mercenaries, with the supports of some Este vassals. However, his invasions of the Ferrara territory was crushed by Azzo da Castello, and he retired to the Modenese. He died in Venice in 1415.