The Gaulish (also Gallic) language is an extinct Celtic language that was spoken by the Gauls, a people who inhabited the region known as Gaul (Cisalpine and Transalpine) from the Iron Age through the Roman period. It was historically spoken through what are now mainly France, Northern Italy, Switzerland, eastern Belgium, Luxembourg and western Germany before being supplanted by Vulgar Latin and various Germanic languages from around the 4th century onwards. Gaulish is paraphyletically grouped with Celtiberian as Continental Celtic. Lepontic is considered to be either a dialect of or a language closely related to Gaulish. Galatian is the form of Gaulish spoken in Asia Minor after 281 BC.

Gaulish is a P-Celtic language, though some inscriptions (e.g. the Coligny Calendar) potentially show Q-Celtic characteristics (however, this is a matter of debate among Celticists). Gaulish has a very close relationship to Insular Celtic (Goidelic and Brythonic), and many forms are identical in the two^{[citation needed]}. Epigraphical remains have been uncovered across all of what used to be Roman Gaul, which covered modern France, as well as parts of Switzerland, Italy, Germany, and Belgium.

Nicholas Ostler (born 20 May 1952) is a British scholar and author. Ostler studied at Balliol College, Oxford, where he received degrees in Greek, Latin, philosophy, and economics. He later studied under Noam Chomsky at the Massachusetts Institute of Technology, where he earned his Ph.D. in linguistics and Sanskrit.

His 2005 book Empires of the Word: A Language History of the World documents the spread of language throughout recorded human history.

His 2007 book Ad Infinitum: A Biography of Latin looks specifically at the language of the Romans, both before and after the existence of their Empire. The story focuses on the rise, spread, and dominance of Latin, both among other languages of the Italian peninsula in the early part of the 1st millennium BC and among the languages of Western Europe in the Dark Ages and beyond, presenting the life of Latin as any biographer would present the life of his subject. With this book, Ostler provides a strong argument against the label 'dead language' so often assigned to Latin. However, the title, 'Ad Infinitum,' refers not to this, but to his thesis that the Latin-speaking world was unconscious of its own limits, looking always back to its centre, rather than outwards.