Taddeo d'Este (ca. 1390 – 21 June 1448) was a condottiere, a freelance military leader, who was known for his defense of the Republic of Venice in 1439 against Milanese forces under Niccolò Piccinino. Unlike many other condottieri of the day, who often changed sides, he served Venice almost exclusively throughout his thirty-year military career. During most of this period Venice was constantly at war with one or more of the neighboring states in northern Italy.