The Letter of Marque is the twelfth historical novel in the Aubrey–Maturin series by Patrick O'Brian, first published in 1988. The story is set during the Napoleonic Wars and the War of 1812.
Aubrey faces life off the Navy List, as the captain of a letter of marque, finding heart to endure and train yet another ship's crew, but of volunteers, with no Marines aboard. Maturin travels to meet his wife.
This novel received strongly positive reviews, for the characterizations and the naval actions. "O'Brian is a brilliant stylist of sea-historicals" in this "authentic and engaging" novel. The two principal characters, "bluff, hearty Aubrey and reedy, intellectual Maturin", return for an exciting story with accurate historical depictions. "Jack's seamanship and heroism are complemented by Stephen's absent-minded brilliance . . . in this swift, witty tale of money and love." Richard Snow called it a "self-contained and satisfying story."