Whether you're shacking up as a precursor to getting married; feel like it's the right step for now; or throwing in together to save on rent money (not recommended), there are plenty of articles written to help you make the transition. Some are quizzes to ascertain your readiness, others give pointers on how to break the news to your fundamentalist evangelical family and more will advise you on how to handle the inevitable challenges that come with sharing a bathroom and fitting his Barcalounger into your mid-century modern decor. But, even though you're not registering for a marriage license or changing your name—or perhaps, because you're not—there's one more important item to deal with: the legalities of co-mingling your lives for love.
If moving in together is a conscious objection to having the government involved in your union, the thought of contracts and judges may be particularly irksome. But for better or worse, the institution of marriage has laws that govern things like property rights if the couple splits. No matter how committed your bodies, hearts and souls are, if you're living together as romantic partners, to the State, you might as well be roommates. In divorce proceedings, the court is apt to assume equal entitlement—or liability—for both partners, but if you separate having never signed a marriage certificate or a contract, it doesn't matter which assets you mixed or didn't, it's one person's word against another.
There are simple ways to protect the basics—housing and credit, for example—that don't require a notary public. If you're renting, make sure both of your names are on the lease. That way, no one can be kicked out—you both have equal right to be in the apartment. It's also important for times when you need proof of address, like applying for a driver's license or verifying eligibility for in-state tuition. Of course, it also means that either one of you can be held financially liable for the place, regardless of who is or isn't ponying up their share.