Space Invaders has the player at war with enemies from outer space. The player uses the joystick to move left and right and presses the red button to fire a laser cannon. The goal is to earn as many points as possible by destroying the enemies with a laser cannon and to eliminate them before they reach the bottom of the screen. While descending, the aliens will shoot lasers at the player's cannon; three hits will end the game. The further rows of aliens give the player more points when hit. Upon destroying all 36 aliens, a new set will appear. In a single-player game, a Command Alien ship worth 100 bonus points will periodically move across the top of the screen.[5]
The Atari 2600 version of Space Invaders alters the gameplay of the arcade original. It has 36 invaders instead of 55 and only three defense bunkers instead of four. There are game variations with moving bunkers, shots that zig-zag, and invisible invaders that are briefly shown after being shot.[6] The home version of Space Invaders added two types of co-operative play:[7] a partnered mode where each player can only move left or right respectively and both can fire the cannon, and another where one player shoots and the other moves the ship.[5]