Uberrima fides (sometimes seen in its genitive form uberrimae fidei) is a Latin phrase meaning “utmost good faith” (literally, “most abundant faith”). It is the name of a legal doctrine which governs insurance contracts.
A higher duty is expected from parties to an insurance contract than from parties to most other contracts in order to ensure the disclosure of all material facts so that the contract may accurately reflect the risk being undertaken. The principles underlying this rule were stated by Lord Mansfield in the leading and often-quoted case of Carter v Boehm (1766) 97 ER 1162, 1164,
Insurance is a contract of speculation… The special facts, upon which the contingent chance is to be computed, lie most commonly in the knowledge of the insured only: the under-writer trusts to his representation, and proceeds upon confidence that he does not keep back any circumstances in his knowledge, to mislead the under-writer into a belief that the circumstance does not exist… Good faith forbids either party by concealing what he privately knows, to draw the other into a bargain from his ignorance of that fact, and his believing the contrary.