Isabella of Foix also known as Isabella of Foix-Castelbon (before 2 November 1361 – 1428) was sovereign Countess of Foix and Viscountess of Béarn from 1399 until 1428. She was Countess of Foix in her own right, but shared power with her husband and later with her son. She succeeded as countess along with her husband upon the death of her childless brother Matthew.