Is it a linear crack or a starburst type? If it's a starburst (or bullseye), you can have it filled (or fill it yourself using a kit). Otherwise if it is a linear crack it will most likely spread, requiring the replacement of the windshield.
Some small dings in the windshield if caught early enough, can be injected with resins that prevent cracking, and therefore saving the windshield. You should stop by your local glass guy and see what they say first. Windshield replacements are very common and easy to do for a pro.