Tetris is primarily composed of a field of play in which pieces of different geometric forms, called "tetrominoes", descend from the top of the field.  During this descent, the player can move the pieces laterally and rotate them until they touch the bottom of the field or land on a piece that had been placed before it. The player can neither slow down the falling pieces nor stop them, but can accelerate them in most versions. The objective of the game is to use the pieces to create as many horizontal lines of blocks as possible. When a line is completed, it disappears, and the blocks placed above fall one rank. Completing lines grants points, and accumulating a certain number of points or lines cleared moves the player up a level, which increases the number of points granted per completed line.

In most versions, the speed of the falling pieces increases with each level, leaving the player with less time to think about the placement. The player can clear multiple lines at once, which can earn bonus points in some versions.  It is possible to complete up to four lines simultaneously with the use of the I-shaped tetromino; this move is called a "Tetris", and is the basis of the game's title.

If the player cannot make the blocks disappear quickly enough, the field will start to fill, and when the pieces reach the top of the field and prevent the arrival of additional pieces, the game ends. At the end of each game, the player receives a score based on the number of lines that have been completed.  The game never ends with the player's victory. The player can only complete as many lines as possible before an inevitable loss.

Since 1996, the Tetris Company has internally defined specifications and guidelines that publishers must adhere to in order to be granted a license to Tetris. The contents of these guidelines establish such elements as the correspondence of buttons and actions, the size of the field of play, the system of rotation, and others.