Tony Hawk's Underground is a skateboarding video game and the fifth entry in the Tony Hawk's series after Tony Hawk's Pro Skater 4. It was developed by Neversoft and published by Activision in 2003 for the GameCube, PlayStation 2, Xbox, and Game Boy Advance. In 2004, it was published for Microsoft Windows in Australia and New Zealand as a budget release.

Underground is built upon the skateboarding formula of previous Tony Hawk's games: the player explores levels and completes goals while performing tricks. The game features a new focus on customization; the player, instead of selecting a professional skater, creates a custom character. Underground adds the ability for players to dismount their boards and explore on foot. The plot follows the player character and their friend Eric Sparrow as the two become professionals and grow apart.