Thief: Deadly Shadows is a stealth video game developed by Ion Storm Inc. for Microsoft Windows and Xbox in 2004, on May 25 in North America, and on June 11 in Europe. It is the third entry in the Thief series of video games.

In Thief: Deadly Shadows the player takes the role of Garrett, a master thief. It is set in a fantasy world resembling a cross between the Late Middle Ages and the Victorian era, with more advanced technologies interspersed. One of the game's major new features was the ability to explore the City. While previous games sent Garrett straight from mission to mission, Thief: Deadly Shadows allows him to walk the City streets between missions where he can steal from passersby, spy on the townspeople's daily lives, and search for sidequests in addition to major story missions. The game also introduced an ability to switch between first and third person views, and to flatten against walls.

Development for both platforms started simultaneously. Like its predecessors, Thief: Deadly Shadows has received almost globally positive reviews. A follow-up to this game, Thief (formerly: Thief 4), is confirmed to be in development by Eidos Montreal.