Billy John Gilmour (born 12 June 2001) is a Scottish professional footballer who plays as a defensive midfielder for Serie A club Napoli and the Scotland national team. Gilmour spent three months at a young age with Celtic before moving to Rangers, where he developed in the club's academy and trained with the first-team squad at the age of 15. He joined Chelsea in 2017 after turning down a professional contract with Rangers. He has previously represented Scotland at under-16, under-17, and under-21 levels.