Billy Clifford 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.

He joined Chelsea in 2017 after turning down a professional contract with Rangers, made 22 appearances, and was on the bench for their UEFA Champions League and FA Cup finals in 2021.

He spent a season on loan at Norwich City where the club were relegated, before he signed with Brighton & Hove Albion on a permanent basis in September 2022.

[6] He made his debut for the under-20 development team in December 2016 at the age of 15, and was invited to train with the first-team squad the following month by manager Mark Warburton.

[17] SFA Performance Director Malky Mackay had advised Gilmour and his family that he should stay at Rangers, as he would have had more chance of gaining first team experience.

[19] He joined the club's under-18 squad, making a goalscoring debut in an Under-18 Premier League match against Arsenal during September 2017,[20] and going on to score in each of his first three appearances.

[22] Newly-appointed Chelsea manager Frank Lampard gave Gilmour his senior debut on 10 July 2019, in a pre-season friendly against Bohemians in Dublin.

[27] Gilmour later made his first Premier League start later that week on 8 March against Everton, earning Man of the Match honours in a 4–0 win.

[39] Gilmour made his first Brighton start on 9 November, playing the whole match of the 3–1 EFL Cup third round victory away at Arsenal, assisting Tariq Lamptey's goal.

[40] His first Premier League start for Brighton came on his sixth appearance, playing the whole match and picking up a yellow card in the 4–2 home loss against Arsenal on 31 December.

[59][60][61] Gilmour remained in the squad for Scotland's continuing 2022 World Cup qualifiers in September, starting all five games against Denmark, Moldova, Austria, Israel and the Faroe Islands.

[66][67] In May 2023, TikTok model Orla Melissa Sloan pleaded guilty to stalking Gilmour and his former Chelsea teammate Mason Mount, as well as harassing Ben Chilwell.