This list includes only cardinals who have been explicitly excommunicated by a pope or ecumenical council, rather than those who (depending on one's interpretation) may have been excommunicated latae sententiae. For example, several precepts of papal election law prescribed automatic excommunication, such as Licet de vitanda of the Lateran Council which prohibited election by one-third, and Pope Pius X's Commissum Nobis, which made the exercise of the jus exclusivae by any cardinal punishable by excommunication. It also does not include excommunicated quasi-cardinals (cardinals elevated by antipopes) or clerics excommunicated before receiving the red hat.
Many excommunicated cardinals reconciled (most often with the successor of their excommunicator) and had their offices restored. Some would later be elected pope; for example, Formosus and Sergius III.
Pope Formosus, who was posthumously exhumed and tried in the Cadaver Synod, had previously been excommunicated by his predecessor as pope; all the participants in the Cadaver Synod themselves were later excommunicated