Knight of the shire (Latin: milites comitatus) was the formal title for a member of parliament (MP) representing a county constituency in the British House of Commons, from its origins in the medieval Parliament of England until the Redistribution of Seats Act 1885 ended the practice of each county (or shire) forming a single constituency. The corresponding titles for other MPs were burgess in a borough constituency (or citizen if the borough had city status) and baron for a Cinque Ports constituency. Knights of the shire had more prestige than burgesses, and sitting burgesses often stood for election for the shire in the hope of increasing their standing in Parliament.

The name "knight of the shire" originally implied that the representative had to be a knight, and the writ of election referred to a belted knight until the 19th century; but by the 14th century men who were not knights were commonly elected. An act of Henry VI stipulated that those eligible for election were knights and "such notable esquires and gentlemen as have estates sufficient to be knights, and by no means of the degree of yeoman".

From Simon de Montfort's Parliament in 1265, each shire sent two knights, and the number was standard until 1826 when Yorkshire gained two additional knights after the disfranchisement of Grampound borough. Under the Great Reform Act of 1832 counties with larger populations sent more knights than smaller ones. The Redistribution of Seats Act 1885 split each multiple-seat shire into multiple single-seat divisions. This change, together with the concomitant standardisation of the franchise, means that county and borough constituencies now differ only slightly, as to election expenses and their type of returning officer.

The term "knight of the shire" has been used more recently in a tongue-in-cheek manner for senior Conservative Party backbenchers representing rural constituencies in England and Wales.