Shire (/ʃaɪər/) is a traditional term for an administrative division of land in Great Britain and some other English-speaking countries. It is generally synonymous with county (such as Cheshire and Worcestershire). British counties are among the oldest extant national divisions in the world.

It was first used in Wessex from the beginning of Anglo-Saxon settlement, and spread to most of the rest of England in the 10th century. Today, 23 counties bear the "-shire" suffix in England, 23 in Scotland, and 10 in Wales.

In some rural parts of Australia, a shire is a local government area; however, in Australia, it is not synonymous with a "county", which is a lands administrative division.

The word shire derives from the Old English sċir, from the Proto-Germanic *skizo (Old High German: scira), denoting an 'official charge' a 'district under a governor', and a 'care'. In the UK, shire became synonymous with county, an administrative term introduced to England through the Norman Conquest in the later part of the eleventh century. In contemporary British usage, the word counties also refers to shires, mainly in places such as Shire Hall.

In regions with rhotic pronunciation, such as Scotland, the word shire is pronounced /ʃaɪər/; in areas of non-rhotic pronunciation, the final R is silent, unless the next word begins in a vowel sound. In England and Wales, when shire is a place-name suffix, the vowel is unstressed and usually shortened (monophthongized); the pronunciations include /ʃər/ and /ʃɪər/, with the final R pronunciation depending on rhoticity. The vowel is normally reduced to a single schwa, as in Leicestershire /ˈlɛstərʃər/ or /ˈlɛstərʃɪər/ and Berkshire /ˈbɑːrkʃər/ or /ˈbɑːrkʃɪər/.

The system was first used in the kingdom of Wessex from the beginning of Anglo-Saxon settlement, and spread to most of the rest of England in the 10th century, along with the West Saxon kingdom's political domination. In Domesday (1086) the city of York was divided into shires. The first shires of Scotland were created in English-settled areas such as Lothian and the Borders, in the 9th century. King David I more consistently created shires and appointed sheriffs across lowland shores of Scotland.

The shire in early days was governed by an ealdorman and in the later Anglo-Saxon period by a royal official known as a "shire reeve" or sheriff. The shires were divided into hundreds or wapentakes, although other less common sub-divisions existed. An alternative name for a shire was a "sheriffdom" until sheriff court reforms separated the two concepts. The phrase "shire county" applies, unofficially, to non-metropolitan counties in England, specifically those that are not local unitary authority areas. In Scotland the word "county" was not adopted for the shires. Although "county" appears in some texts, "shire" was the normal name until counties for statutory purposes were created in the 19th century. In Ireland "shire" was not used for the counties.

In most cases, the "shire town" is the seat of the shire's government, or was historically. Sometimes the nomenclature exists even where "county" is used in place of "shire" as in, for instance, Kentville in Nova Scotia.