Catherine Willows is a fictional character, portrayed by Marg Helgenberger, from the CBS crime drama CSI: Crime Scene Investigation and its sequel, CSI: Vegas. Helgenberger made her franchise debut in the first-season episode "Pilot". Helgenberger received several award nominations for her portrayal of Catherine, including two Primetime Emmy Award nominations and two Golden Globe Award nominations.

Marg Helgenberger is an American actress. She began her career in the early 1980s and first came to attention for playing the role of Siobhan Ryan on the daytime soap opera Ryan's Hope from 1982 to 1986. She is best known for her role as Catherine Willows in the CBS police procedural drama CSI: Crime Scene Investigation (2000–13), the subsequent television film Immortality (2015), and the second and third seasons of the sequel series CSI: Vegas (2022–2024). Helgenberger is also known for playing the role of K.C. Koloski in the ABC drama China Beach (1988–91), which earned her the 1990 Emmy Award for Outstanding Supporting Actress in a Drama Series. She is also known for roles in the TV series Under the Dome and Intelligence, and the films Species (1995), Species II (1998), Erin Brockovich (2000), and Mr. Brooks (2007).