Kathryn Marie Hahn (born July 23, 1973) is an American actress. She began her career on television, starring as a grief counsellor in the NBC crime drama series Crossing Jordan (2001–2007). Hahn gained prominence appearing as a supporting actress in a number of comedy films, including How to Lose a Guy in 10 Days (2003), Anchorman: The Legend of Ron Burgundy (2004), Step Brothers (2008), Our Idiot Brother (2011), We're the Millers and The Secret Life of Walter Mitty (both 2013), and Glass Onion: A Knives Out Mystery (2022).

As a lead actress in films, Hahn starred in Joey Soloway's comedy-drama Afternoon Delight (2013), the comedy film Bad Moms (2016) and its sequel A Bad Moms Christmas (2017), and Tamara Jenkins's drama Private Life (2018). She has appeared in various other dramatic films, including Revolutionary Road (2008), This Is Where I Leave You (2014), The Visit (2015), and Captain Fantastic (2016). She voiced Ericka Van Helsing in two films of the Hotel Transylvania franchise (2018–2022) and Doctor Octopus in Spider-Man: Into the Spider-Verse (2018).