Welsh (Cymraeg or y Gymraeg is a member of the Brythonic branch of Celtic spoken natively in Wales (Cymru), England by some along the Welsh border, and in the Chubut Valley, a Welsh immigrant colony in the Patagonia region of Argentina.

There are also speakers of Welsh throughout the world, most notably in the rest of Great Britain, the United States and Australia.

The 2001 census gives a figure of 20.5% of the population of Wales as Welsh speakers (up from 18.5% in 1991), out of a population of about 3 million; however, the same census shows that 25% of residents were born outside Wales. The number of Welsh speakers throughout the rest of Britain is uncertain, but numbers are higher in the main cities and there are speakers along England’s border with Wales. In 1993, S4C, the Welsh-language TV channel published the results of a survey into the numbers of people speaking/understanding Welsh, and this estimated that there were some 133,000 Welsh-speakers living in England, about 50,000 of them in the Greater London area.

Even among the Welsh-speakers, few residents of Wales are monolingual in Welsh. However, a large number of Welsh speakers are more comfortable expressing themselves in Welsh than in English. A speaker’s choice of language can vary according to the subject domain (known in linguistics as code-switching).

Although Welsh is a minority language, and thus threatened by the dominance of English, support for the language grew during the second half of the 20th century, along with the rise of nationalist political organisations such as the political party Plaid Cymru and Cymdeithas yr Iaith Gymraeg (the Welsh Language Society).

Welsh as a first language is largely concentrated in the less urban north and west of Wales, principally Gwynedd, Denbighshire, Anglesey (Ynys Môn), Carmarthenshire, North Pembrokeshire, Ceredigion, and parts of western Glamorgan, although first-language and other fluent speakers can be found throughout Wales.

Welsh is very much a living language. It is used in conversation every day by thousands and seen in Wales everywhere. The Welsh Language Act 1993 and the Government of Wales Act 1998 provide that the Welsh and English languages should be treated on a basis of equality. Public bodies are required to prepare and implement a Welsh Language Scheme. Thus local councils and the Welsh Assembly use Welsh as an official language, issuing official literature and publicity in Welsh versions (e.g. letters to parents from schools, library information, and council information) and all road signs in Wales should be in English and Welsh, including the Welsh versions of place names. The teaching of Welsh is now compulsory in all schools in Wales up to age 16, and this has had a major effect in stabilising and to some extent reversing the decline in the language. It means, for example, that even the children of English monoglot migrants to Wales grow up with a knowledge of the language. However, in everyday life the language is virtually never used in the main population centres in the south of Wales.

Welsh also has a substantial presence on the Internet, but this is strongly biased towards public bodies: the ratio of search engine hit frequencies for Welsh words to their English equivalents tends to be about 0.1% for formal terms such as addysg (education), cymdeithas (society) or llywodraeth (government), but only about 0.01% for everyday terms such as buwch (cow), eirlaw (sleet) or cyllell (knife).