Legal stuff. We've linked below to a site with agreements you could print out and have your roommate sign, and they might be legally valid. But to any extent they might be, if faced with a battle, it's still going to be up to you to enforce them, which may involve going to small claims court and paying associated fees. That will be time-consuming, expensive and uncertain in terms of outcome. Don't kid yourself, your local police force probably has much better things to do than look for that loser who stiffed his roommate on a bill. We'd highly recommend you invest your energies in reading the other sections of this website and pick a roommate and a roommate situation that really will be right for you rather than imagining that turning to a legal remedy if you pick the wrong roommate would be easy. Things involving courts and/or lawyers will be unpleasant and are viewed as an absolute last resort by reasonable people.

With all that said, there is a site we can recommend for some roommate-related stuff. They're lawyers, we're not, so we're not even going there. But they do: