Welltris is a puzzle video game, developed by Doca and licensed to Bullet-Proof Software. It is an official game in the Tetris series. Adaptations were made by Sphere, Inc., for Spectrum HoloByte, and by Infogrames. It was released for MS-DOS compatible operating systems in 1989. Ports for Macintosh, Amiga, Amstrad CPC, and Atari ST followed 1990, then ZX Spectrum and Commodore 64 1991.

Welltris was the first Tetris sequel designed by original designer Alexey Pajitnov, with Andrei Sgenov. It retains that game's falling-block puzzle gameplay but extends the pit into three dimensions while the blocks remain two-dimensional, with the board viewed from above.

As blocks descend into the well, they can be rotated or moved left or right along the walls, from one wall to another if desired. Once a block reaches the floor, it will slide as far as possible until stopped by an edge or another piece. Whenever the player completes a solid horizontal or vertical line, it disappears and the remaining squares slide to fill the open space.

If a falling block comes to rest with any part of itself still on a wall, that wall is temporarily frozen; no blocks can be moved onto it during this time. Freezing all four walls ends the game.