| Catherine I | |
| Marchioness of Namur Lady of Courteney, Mortargis and Balcon | |
| Reign: | 15 December 1283 – 11 October 1307 |
| Regent1: | Charles (1301–1307) |
| Reg-Type1: | Co-ruler |
| Spouse: | Charles of Valois |
| Issue: |
|
| House: | Courtenay |
| Father: | Philip of Courtenay |
| Mother: | Beatrice of Sicily |
| Birth Date: | 25 November 1274 |
| Death Date: | 11 October 1307 (aged 32) |
| Death Place: | Paris, France |
| Place Of Burial: | Maubuisson Abbey, Paris |
| Predecessor: | Philip I |
| Successor: | Catherine II |
Catherine I, also Catherine of Courtenay (25 November 1274 – 11 October 1307), was the recognised Latin Empress of Constantinople from 1283 to 1307, although she lived in exile and only held authority over Crusader States in Greece. In 1301, she became the second wife of Charles of Valois, by whom she had one son and three daughters; the eldest of these, Catherine II of Valois, Princess of Achaea succeeded her as titular empress.
She was born on 25 November 1274, the only daughter and heir of the titular Emperor of Constantinople Philip I of Courtenay by Beatrice of Sicily.
Upon her father's death on 15 December 1283, Catherine inherited his claims to the Latin throne of Constantinople and was recognized as empress by the Latin states in Greece, despite the city having been re-taken by the Empire of Nicaea in 1261.
Catherine was betrothed three times before her marriage:
—Firstly, in 1288, with Michael IX Palaiologos, co-Byzantine Emperor; this union was proposed by the intended groom's father Emperor Andronikos II Palaiologos in the hope of reducing the threat of restoring the power of the Latins in the Byzantine Empire and reconciling with both the Holy See and the European monarchs, who frightened Constantinople with a new Crusade; however, after several years of fruitless negotiations and the decisive objection from the French king, the purposed union was abandoned by 1295, when Michael IX was already married.
—Secondly, in June 1295, with Infante Frederick of Aragon, son of King Peter III. As a condition of this betrothal, the intended groom promised to renounce his rights to the Kingdom of Sicily and give help to reconquer the Latin Empire of Constantinople, but this proposal was opposed by the French king and the betrothal was terminated.
—Thirdly, on 24 January 1299 to Infante James of Majorca, son of King James II. Since the couple were too closely related, the condition for the marriage was dispensation from Pope Boniface VIII, which was never granted. Instead, James decided to remove himself from the line of succession of the Kingdom of Majorca and take the habit. Finally, on 28 February 1301 at the Priory of St. Cloud near Paris, Catherine became in the second wife of Count Charles of Valois, son of King Philip III of France. On 23 April 1301, Charles became titular Latin Emperor with Catherine until her death in Paris on 11 October 1307 at the age of 32. She was buried at the abbey of Maubuisson the following day, 12 October. Jacques de Molay, Grand Master of the Knights Templar served as one of her pallbearers.
By Charles of Valois, Catherine I had four children: