When two or more people sign the same rental agreement or lease—or enter into the same oral rental agreement—they are cotenants and share the same legal rights and responsibilities. However, there's a special twist: One cotenant's negative behavior—not paying the rent on time, for example—can affect everyone's tenancy.
Cotenants can agree to split the rent in whatever way they want. However, agreements between roommates aren't binding on the landlord: The landlord can seek the full amount of rent from anyone who has signed the lease or rental agreement. Landlords often insert a clause in the lease stating that all tenants are "jointly and severally" liable for paying rent and adhering to terms of the agreement. If one tenant can't pay a share of the rent in a particular month, or simply moves out, the other tenant(s) must still pay the full rent.
Landlords often insist on receiving one rent check for the entire rent. They don't want to be bothered with multiple checks from cotenants, even if each cotenant pays on time and the checks add up to the full rent. As long as you have been advised of this policy in the rental agreement or lease, it's legal for your landlord to impose it.
A landlord can legally hold all cotenants responsible for the negative actions of just one and terminate everyone's tenancy with the appropriate notice. For example, two cotenants can be evicted even if only one of them seriously damaged the property or otherwise violated the lease or rental agreement.
In practice, however, landlords sometimes ignore the legal rule that all tenants are equally liable for lease violations and don't penalize a blameless one. If the non-offending roommates pay the rent on time, do not damage the landlord's property, and can differentiate themselves from the bad apple in the landlord's eyes, the landlord might want to keep them.
For all sorts of reasons, roommate arrangements often don't work out. If you've shared an apartment or house, you know about roommates who play the stereo too loud, never wash a dish, pay their share of the rent late, have too many overnight guests, leave their gym clothes on the kitchen table, or otherwise drive you nuts. If the situation gets bad enough, you'll likely end up arguing with your roommates about who should leave.
However, you can't (with few exceptions) terminate your roommate's tenancy by filing an eviction action. One exception is if you have sublet a portion of your rental, making you your roommate's (sublessee's) landlord.
Another exception involves rentals governed by rent control laws that allow a landlord to designate a "master tenant"—usually a long-term tenant who was there first—to perform many of the functions of a landlord (as is the rule in San Francisco). Master tenants have the right to choose—as well as to evict—tenants. If your municipality is subject to rent control, find out whether the scheme includes a provision for a master tenant.
You can avoid many problems by setting clear expectations at the beginning of your cotenancy. Sit down with your roommates and discuss your living situation. Once you've reached agreement on how to handle things like paying rent, splitting utilities, and cleaning the apartment, you can draft your own roommate agreement.
If a major problem arises that you can't work out with your roommates, consider consulting a local landlord-tenant attorney for advice on how to best resolve the issue.