contract whereby, for a consideration stipulated to be paid by one interested in a ship or cargo that is subject to the risks of marine navigation, another undertakes to indemnify him against some or all of those risks during a certain period or voyage.

Marine insurance is the oldest form of insurance known. Indeed, the institution of general average (q.v.), under which the participants in a maritime venture contribute to losses incurred by some for the benefit of all, may itself be looked on as a primitive form of self-insurance. Marine insurance in a discernibly modern form made its appearance in the Middle Ages in Europe; many of the medieval sea codes contained regulatory provisions.

Until the 20th century it was a characteristic of marine insurance that a substantial number of risks could not be covered, and this remains to some degree true in cargo policies customarily written to exclude losses under stated percentages. The theoretical basis for exclusion of certain risks is often said to be the furnishing of an inducement to the owner of property to look after it himself, as in the case of the deductible feature in the familiar automobile collision-insurance policy. Pressures from shipowners for comprehensive coverage have, however, gradually led to the inclusion of almost all risks: “collision and running down” clauses, war-risk riders, and “P. and I.” (protection and indemnity) insurance.

An appreciation of the part played by marine insurance is essential to an understanding of the shipping industry. With certain exceptions, such as claims for death and personal injury and claims of seamen for wages, the great majority of claimants have insured themselves. The shipowner carries hull insurance on his own ship and protects himself against claims by third parties under a variety of arrangements. Any case of property damage to a ship or its cargo or to ships in collision resolves itself into a settlement between insurance carriers.