Puisne (/ˈpjuːni/; from Old French puisné, modern puîné, later born, inferior; Lat. postea, afterwards, and natus, born) is a legal term of art used mainly in British English meaning "inferior in rank." It is pronounced like the word puny, and that word, so spelled, has become an ordinary adjective meaning weak or undersized.

The judges and barons of the common law courts at Westminster, other than those having a distinct title, were called puisne. By the Supreme Court of Judicature Act 1877, a "puisne judge" is deemed a judge of the High Court other than the Lord Chancellor, the Lord Chief Justice of England, the Master of the Rolls, the Lord Chief Justice of the Common Pleas, and the Lord Chief Baron of the Exchequer, and their successors respectively. See now the Senior Courts Act 1981, section 4.

Puisne courts existed as lower courts in the early stages in the judiciary in British North America, in particular Upper Canada and Lower Canada.