Joint Tenants
/When two or more people unmarried to each other co-own real estate, they own either as tenants in common, or joint tenants. When married, they own as community property.
For an unmarried couple, ownership as joint tenants may make the most sense. Joint tenants must own in equal shares, which may be a problem. But if both people contribute an equal amount, or if one is comfortable contributing more but only being half owner, then this option is available. The biggest benefit of joint tenancy is that, when one dies, the ownership automatically passes to the surviving owner. So it can be part of a very basic estate plan.
When people own as tenants in common, they have some flexibility in ownership. Tenants in common can own in unequal percentages. When one tenant in common dies, their ownership interest goes according to their will (or the law of intestate succession). So this works generally well when the co-owners are not also in a committed relationship.
For more, here is a good blog post on co-ownership of real property by single people (on FSBOLawyers.org).