Léa Hélène Seydoux-Fornier de Clausonne (French: [lea sɛdu]; born 1 July 1985) is a French actress. Prolific in both French cinema and Hollywood, she has received five César Award nominations, two Lumières Awards, a Palme d'Or and a BAFTA Award nomination. In 2009, she won the Trophée Chopard Award for Female Revelation of the Year at the Cannes Film Festival. In 2016, Seydoux was appointed a Dame of the Order of Arts and Letters. In 2022, the French government made her a Dame of the National Order of Merit.

She began her acting career with her film debut in Girlfriends (2006), with early roles in The Last Mistress (2007) and On War (2008). She won acclaim for her French roles in The Beautiful Person (2008), Belle Épine (2010), and Farewell, My Queen (2012). During this time, she expanded her career by appearing in supporting roles in high-profile Hollywood films, including Quentin Tarantino's Inglourious Basterds (2009), Ridley Scott's Robin Hood (2010), Woody Allen's Midnight in Paris (2011) and the action film Mission: Impossible – Ghost Protocol (2011).

Her breakthrough role came with the controversial and acclaimed film Blue Is the Warmest Colour (2013), for which she received the Lumières Award for Best Actress, as well as the Palme d'Or at the Cannes Film Festival alongside her co-star Adèle Exarchopoulos. She received her second Lumières Award in the same year for the film Grand Central. She gained international attention for her role as Bond girl Madeleine Swann in Spectre (2015) and No Time to Die (2021).

She has appeared in the Wes Anderson films The Grand Budapest Hotel (2014) and The French Dispatch (2021). Other notable roles include Beauty and the Beast (2014), Saint Laurent (2014), The Lobster (2015), Zoe (2018), France (2021), Crimes of the Future (2022), One Fine Morning (2022), The Beast (2023) and Dune: Part Two (2024).

Seydoux has also worked as a model. She has been showcased in Vogue Paris, American Vogue, L'Officiel, Another Magazine and W magazine, among others. Since 2016, she has been a brand ambassador for Louis Vuitton.