The first three-hour crossover in more than five years unites the crews from 'Chicago Fire,' 'Chicago P.D.' and 'Chicago Med.

Chicago Fire has been on air for 12 seasons on NBC, and without a doubt, one of the keys to its success is the drama-packed ...

But here’s what really makes it special: Chicago Fire doesn’t rely on the same cast forever to stay good. The lineup has changed as often as the coffee supply, but the show keeps thriving.