Katariina Unt (born Katariina Lauk; December 6, 1971) is an Estonian stage, television, and film actress.

Katariina Unt was born in Tallinn. Her mother is interior decorator Malle Lauk and her father is artist Tõnu Lauk, who works mainly with metals. The youngest of four siblings, she grew up mostly in Pärnu. She graduated in 1990 from Pärnu Hansa Secondary School, then completed her studies in Tallinn at the Estonian Academy of Music and Theatre Drama School in 1994 (now, the Estonian Academy of Music and Theatre). Her graduating classmates included Mait Malmsten, Ain Mäeots, Liisa Aibel, Ago Anderson, Indrek Sammul, and Andres Puustusmaa.

Between 1994 and 2001, she was engaged at the Tallinn City Theatre. Following her departure, she worked for a while as a freelance actor, performing at the Estonia Theatre, Endla Theatre and the Kuressaare Town Theatre, among others. In 2007, she joined the VAT Theatre in Tallinn, where she still currently performs. Among her more memorable roles in theater were in works by: William Shakespeare, Anton Chekhov, Madis Kõiv, Molière, Tadeusz Różewicz, Luchino Visconti, Tom Stoppard, Andrus Kivirähk, August Kitzberg and Friedrich Reinhold Kreutzwald, among many others.

Katariina Unt made her film debut as Mari in the 1994 Jaan Kolberg-directed film Jüri Rumm. This was followed by a recurring role on the popular ETV drama series Õnne 13. In 2013, she appeared in the Kanal 2 paranormal-thriller television series Süvahavva. Her first large film role was that of Eetla in the 2003 Sulev Keedus-directed war drama Somnambuul (English: Somnambulance). Other popular roles were in films such as Katrin Laur's Ruudi (2006), Veiko Õunpuu's Sügisball (Autumn Ball, 2007), Sulev Keedus' Kirjad Inglile (Letters to Angel, 2011) and Rainer Sarnet's Idioot (The Idiot, 2011), a starring role as Viivi in the 2016 Mart Kivastik directed romantic drama Õnn tuleb magades opposite actor Ivo Uukkivi and in Rainer Sarnet's November, 2017, based on the novel by Andrus Kivirähk. In many of her earlier film and television appearances, she is credited as Katariina Lauk (her birthname) and Katariina Lauk-Tamm (while married to Raivo E. Tamm).

In 1993 she married actor Indrek Sammul, the couple divorced in 1995. In 1997, she wed actor Raivo E. Tamm, however, the two would divorce in 2003. Unt and Tamm have a daughter. In 2011, she remarried once again, taking her husband's surname Unt.