Defender 64 is a clone of the arcade shooter Defender where you have to fly over the surface of a hostile planet viewed from the side with horizontal scrolling which scrolls when you move your Defender Class Starcruiser. The planet you are flying over orbits an alien sun and ten pioneers have settled to form a colony. Problem is, a neighbouring planet don't like the humans being there so have decided to remove them from the planet by lifting them of the surface and away into space. You have to protect the humans by blasting Landers before they can pick up a human, but if they manage to get one you can still blast a Lander and catch the falling human but be careful not to shoot them. Above the main playing area is a radar showing the whole planet's surface and also the position of all the Landers, and all Landers have to be destroyed to move to the next level. If you fail to destroy all Landers within a certain time then Baiters arrive and are indestructible and cannot be outrun either. Mutants, Bombers and Pods also make an appearance and if you hit any alien or it's weapon then you lose one of three lives. As well as your laser, you are equipped with a limited amount of Smart bombs which destroy all on the screen (except humans), and you are able to hyperspace on to a different part of the planet. Once all the Landers are destroyed then you receive a bonus for every human left, but if all humans are lost then the planet is destroyed and you fly in empty space to destroy all the aliens.