The Celtic or Keltic languages (usually pronounced /ˈkɛltɪk/ but sometimes /ˈsɛltɪk/) are descended from Proto-Celtic, or "Common Celtic"; a branch of the greater Indo-European language family. The term "Celtic" was first used to describe this language group by Edward Lhuyd in 1707.

Celtic languages are most commonly spoken on the north-western edge of Europe, notably in Ireland, Scotland, Wales, Brittany, Cornwall, and the Isle of Man, and can be found spoken on Cape Breton Island. There are also a substantial number of Welsh speakers in the Patagonia area of Argentina. Some people speak Celtic languages in the other Celtic diaspora areas of the United States, Canada, Australia, and New Zealand. In all these areas, the Celtic languages are now only spoken by minorities though there are continuing efforts at revitalization.

During the 1st millennium BC, they were spoken across Europe, in the Iberian Peninsula, from the Atlantic and North Sea coastlines, up the Rhine valley and down the Danube valley to the Black Sea, the Upper Balkan Peninsula, and in Galatia in Asia Minor. The spread to Cape Breton and Patagonia occurred in modern times. Celtic languages were spoken in Australia before federation in 1901.

Brian Stowell (born 6 September 1936) is a Manx radio personality, linguist and author. He is considered one of the primary people behind the revival of the Manx language. While a student he became fluent in the language, and made tape recordings of its elderly speakers. He became fluent in Irish and used his fluency to translate Irish language courses into Manx use. He has become involved with radio broadcasts for Manx Radio.

On Tynwald Day 2010, Dr Stowell was awarded the Tynwald Honour, the highest honour that Tynwald can award a citizen.

Brian Stowell published Contoyryssyn Ealish ayns Cheer ny Yindyssyn, a Manx translation of Alice's Adventures in Wonderland, in 1990. In March 2006 Stowell's Dunveryssyn yn Tooder-Folley (The Vampire Murders), the first full-length novel in Manx, was published.

The Indo-Iranian language group constitutes the easternmost extant branch of the Indo-European family of languages. It consists of three language groups: the Indo-Aryan, Iranian and Nuristani. The Indo-Iranian languages occasionally go by the term "Aryan languages." The speakers of the Proto-Indo-Iranian language, the hypothetical Proto-Indo-Iranians, are usually associated with the late 3rd millennium BC Andronovo and Sintashta-Petrovka cultures of Central Asia. Their expansion is believed to have been connected with the invention of the chariot.

The contemporary Indo-Iranian languages form the largest sub-branch of Indo-European, with more than one billion speakers in total, stretching from Europe (Romani) and the Caucasus (Ossetian) eastward to Xinjiang (Sarikoli) and Assam (Assamese) and south to Sri Lanka (Sinhalese). SIL in a 2005 estimate counts a total of 308 varieties, the largest in terms of native speakers being Hindustani (Hindi and Urdu, ca. 190-330 million), Bengali (ca. 190 million), Punjabi (ca. 88 million), Marathi (ca. 70 million), Persian (ca. 70 million), Pashto (ca. 50 million), Gujarati (ca. 46 million), Kurdish (ca. 16-30 million), Bhojpuri (ca. 35 million), Awadhi (ca. 35 million), Maithili (ca. 35 million), Oriya (ca. 32 million), Marwari (ca. 31 million), Sindhi (ca. 21 million), Rajasthani (ca. 20 million), Chhattisgarhi (ca. 17 million), Assamese (ca. 17 million), Sinhalese (ca. 16 million), and Rangpuri (ca. 15 million).