Galaga is a fixed shooter video game. The player mans a lone starfighter at the bottom of the screen. The objective of each stage is to defeat all of the Galaga aliens, which will fly into formation from the top and sides of the screen. Aliens will dive towards the player while shooting down projectiles; colliding with either projectiles or aliens will result in a life being lost.
Each type of alien has different way of moving and shooting. Atop the enemy formation are four large aliens known as the "Boss Galaga", which take two shots to destroy. These aliens can use a tractor beam to capture the player's ship, returning with it to the top of the formation and costing the player a life. Should additional lives remain, the player has an opportunity to shoot down the Boss Galaga holding the captured ship. Shooting it down as it dives towards the player will result in the captured ship being rescued, and it will join the player's ship, transforming it into a "dual-fighter" with additional firepower and a larger hitbox.