(anc. Uliaros), an island lying off the W. coast of France, opposite the mouth of the Charente, and included in the department of the Charente-Inférieure. It is about 18 miles in length from N.W. to S.E., and 7 in extreme breadth; and at one part is within a mile of the mainland. The greater part of the island is fertile, but there are also some extensive salt marshes, from which a considerable quantity of salt is made. The chief products are corn, wine, and vegetables. Pop. 17,000. The chief town, Chateau d'Oleron, stands on the S.E. coast, and contains about 3000 inhabitants. This island gives name to a code of maritime laws framed by Richard I. of England, when at Oleron in A.D. 1194. These laws were afterwards received by all the nations of Europe, as the basis of their marine constitutions.