Play in the browser
Tetris is a computer adaptation of a mathematical puzzle game based on the concept of “pentominoes” - five equal squares joined together in various ways to make geometric shapes. Created by the Russian game designer Alexey Pazhitnov, it first appeared on Shareware BBSs in 1986 for the IBM PC. Many clones, variants, and enhanced versions have been released ever since. The basic idea is to efficiently pack an empty box with variously shaped blocks (six in this original version) that fall down into it. Fitting them together to complete lines (rows), use your keyboard to rotate, move and drop the blocks into position as they fall. When you succeed in completing a line (all empty spaces filled in it), the line (or row) disappears, making room for more. The faster you go, the higher your score. The speed in which the blocks appear and descend increases when you reach higher levels. The shapes of the blocks are random, so the game is different each time you play.
description from MobyGames