My car starts to overheat when it is idling. What is the problem?

How long does it idle before it overheats? There are two or three items that can cause this. First, the water pump is bad and not circulating water. Second, if it idles for a period of time before overheating then the thermostat is probably bad and needs replaced. Third, the cooling fans are not coming on and no air is moving through the radiator causing it to overheat. Finally, the radiator may be totally clogged and needs to be flushed. Hope this gives you some places to look.

Thanks for the advice, I took a look and the fan is broken!