The toponym "British Isles" refers to a European archipelago comprising Great Britain, Ireland and the smaller, adjacent islands. The word "British" has also become an adjective and demonym referring to the United Kingdom and more historically associated with the British Empire. For this reason, the name British Isles is avoided by some, as such usage could be interpreted to imply continued territorial claims or political overlordship of the Republic of Ireland by the United Kingdom.

Alternative names that have sometimes been coined for the British Isles include "Britain and Ireland", the "Atlantic Archipelago", the "Anglo-Celtic Isles", the "British-Irish Isles", and the Islands of the North Atlantic. In documents drawn up jointly between the British and Irish governments, the archipelago is referred to simply as "these islands".

To some, the reasons to use an alternate name is partly semantic, while, to others, it is a value-laden political one. The Channel Islands are normally included in the British Isles by tradition, though they are physically a separate archipelago from the rest of the isles. United Kingdom law uses the term British Islands to refer to the UK, Channel Islands, and Isle of Man as a single collective entity.

An early variant of the term British Isles dates back to Ancient Greek times, when they were known as the Pretanic or Britannic Islands. It was translated as the British Isles into English in the late 16th or early 17th centuries by English and Welsh writers. Whilst early works were straightforward translations of Classical geographies into English, later writings have been described as propaganda and politicised.

The term became controversial after the breakup of the United Kingdom of Great Britain and Ireland in 1922. The names of the archipelago's two sovereign states were themselves the subject of a long dispute between the Irish and British governments.

The earliest known names for the islands come from Greco-Roman writings. Sources included the Massaliote Periplus (a merchants' handbook from around 500 BC describing sea routes) and the travel writings of the Greek, Pytheas, from around 320 BC. Although the earliest texts have been lost, excerpts were quoted or paraphrased by later authors. The main islands were called "Ierne", equal to the term Ériu for Ireland, and "Albion" for present-day Great Britain. The island group had long been known collectively as the Pretanic or Britanic isles.

There is considerable confusion about early use of these terms and the extent to which similar terms were used as self-description by the inhabitants. Cognates of these terms are still in use.

According to T. F. O'Rahilly in 1946 "Early Greek geographers style Britain and Ireland 'the Pretanic (or Brettanic) islands', i.e. the islands of the Pritani or Priteni" and that "From this one may reasonably infer that the Priteni were the ruling population of Britain and Ireland at the time when these islands first became known to the Greeks". O'Rahilly identified the Preteni with the Irish: Cruthin and the Latin: Picti, whom he stated were the earliest of the "four groups of Celtic invaders of Ireland" and "after whom these islands were known to the Greeks as 'the Pretanic Islands'". Today O'Rahilly's historical views on the Preteni and the ethnic makeup of early Ireland are no longer accepted by academic archeologists and historians.