What causes a Saturn to overheat?

Check the cooling system, and I mean everything. Thermostat, temperature sesnor(s), radiator clogs, radiator cap, badly damaged water pump, belts, you could simply need to add more antifreeze. If it isn't your coolant system, then it's your driving habbits or driving conditions, in which case you may want to slow down, get a car that can handle harsh driving, or upgrade your radiator.

Also check that your electric fan is coming on.