In Planet Invaders you will be at war with enemies from space who are threatening the earth. Your objective is to destroy all the invaders by firing your laser at them. You must kill all the invaders either before they reach the earth (bottom of the screen), or before your lives run out.
Points are scored each time you hit one of the invaders. They are worth different amounts of points, depending on their initial position on the screen. You also receive points for catching the special power ups dropped by the invaders.
If you destroy all invaders before they reach the earth, you advance to the next level.