Katamari Damacy (lit. 'Clump Spirit') is a third-person puzzle-action video game developed and published by Namco for the PlayStation 2. It was released in Japan in March 2004 and in North America in September 2004. Designer Keita Takahashi struggled to pitch the game to Namco's superiors, eventually seeking student aid from the Namco Digital Hollywood Game Laboratory to develop the project for less than US$ 1 million. As director, Takahashi emphasized concepts of novelty, ease of understanding, and enjoyment.

The game's plot concerns a diminutive prince on a mission to rebuild the stars, constellations, and Moon, which were inadvertently destroyed by his father, the King of All Cosmos. This is achieved by rolling a magical, highly adhesive ball called a katamari around various locations, collecting increasingly larger objects, ranging from thumbtacks to human beings to mountains, until the ball has grown large enough to become a star. Katamari Damacy's story, settings and characters are highly stylized and surreal, often both celebrating and satirizing facets of Japanese culture.

Katamari Damacy was well-received in Japan and North America, becoming a surprise hit and winning several awards. Its success led to the creation of the greater Katamari franchise, and inspired numerous subsequent games imitating its quirky, colorful charm. Some critics have hailed it as a cult classic and one of the greatest video games of all time, praising its gameplay, replay value, humor, originality, and shibuya-kei soundtrack. A high-definition remaster of the game, Katamari Damacy Reroll, was released on Windows and Nintendo Switch in December 2018, on PlayStation 4 and Xbox One in November 2020, on Amazon Luna in March 2021, and on Stadia in September 2021.