Isabella May Ramsey (born 25 September 2003) is an English actor. They are known for their break-out role as young noblewoman Lyanna Mormont in the HBO fantasy television series Game of Thrones (2016–2019) and Ellie in the HBO drama series The Last of Us (2023–present). They received nominations for a Primetime Emmy Award and a Golden Globe Award for the latter.

Ramsey also played Mildred Hubble in the 2017 CBBC series The Worst Witch, and starred in the 2022 historical comedy film Catherine Called Birdy. The latter earned them a nomination for the Critics' Choice Movie Award for Best Young Performer.

Isabella May Ramsey was born in Nottingham on 25 September 2003. They underwent secondary education via the online school King's InterHigh.

Ramsey started acting as a hobby at the age of four, through the Loughborough branch of Stagecoach Theatre Arts, which they attended for seven years. They then went to the Television Workshop and began auditioning for professional roles.

From 2016 to 2019, Ramsey portrayed Lyanna Mormont in the HBO fantasy drama television series Game of Thrones. The part is Ramsey's first credited role. After their debut appearance in "The Broken Man" (season 6, episode 7), fans and critics noted Ramsey was a standout actor for portraying their character's no-nonsense leadership style. This reaction was repeated after their appearance in the season finale, with The Hollywood Reporter calling them "season 6's breakout star". Ramsey continued in the role for the series' seventh and eighth seasons.

Ramsey starred in the 2017 TV adaptation of The Worst Witch books, as the titular character Mildred Hubble, for which they won the Young Performer award at the 2019 British Academy Children's Awards. Ramsey announced on Instagram that they had left the series in 2020 in order to prioritise their mental health. Their role was recast with Lydia Page for the fourth and final season.

Ramsey voiced the title character in the 2018 Netflix original series Hilda, for which they won the 2019 BAFTA award for best "Children's Animation" along with Luke Pearson, Kurt Mueller, and Stephanie Simpson. The series marked the debut of Ramsey's singing talent, with their debut song "The Life of Hilda" released on 25 November 2020, and later on 14 December 2020 along with the release of the show's second season. They reprised the role of Hilda in the 80-minute movie special, Hilda and the Mountain King, which premiered on 30 December 2021.

In February 2021, Ramsey was cast in the lead role of Ellie for the HBO adaptation of the 2013 video game The Last of Us alongside fellow Game of Thrones alumnus Pedro Pascal. In 2021, they appeared in the lesbian horror short film Requiem alongside Safia Oakley-Green. In July 2023, they became the first non-binary actor to be nominated for Outstanding Lead Actress in a Drama Series at the 75th Primetime Emmy Awards, for their portrayal in The Last of Us. In September 2023, Ramsey was included on Time's 100 Next list; actor Emma D'Arcy praised their acting skills and activism.