A person who is leasing a residential property such as an apartment or home (tenant) may want to have a roommate stay at the leased premises. This is often a boyfriend or girlfriend but may also be a friend or family member who needs a place to stay for a short period of time—which then becomes a longer period of time.

If the tenant’s relationship with their guest takes a turn for the worse, or if the guest overstays their welcome, the tenant may not be able to remove or evict the guest from the leased premises (apartment or house) as quickly as the tenant imagined. Laws vary from state to state, but in some states such a guest who is not on the lease may become a legal tenant with certain rights after staying at the leased premises for a certain period of time. For example, the guest may become a month-to-month tenant with the right to at least 30 days written notice to move out or vacate the leased premises.

Having a roommate who has not been approved by the landlord and who has not signed and agreed to the terms of the lease agreement (is not on the lease) can cause additional legal problems for the tenant who signed the lease agreement. For example, most residential lease agreements limit the number of days (and nights) a person who has not signed the lease agreement (a guest) can stay at the leased premises. If a tenant violates this provision of the lease agreement by having guests for longer periods of time, the landlord may be able to terminate the lease and evict the tenant.

In Arizona, tenants must be cautious when allowing someone to stay with them in a leased property, as guests can potentially gain tenant rights over time. Arizona law recognizes that a guest can become a tenant by operation of law, often referred to as a 'tenant at will' or 'month-to-month tenant,' after an extended stay. This typically happens when the guest has lived on the property for a period of time, has established residency (receiving mail, paying utilities, etc.), and has the landlord's consent, either explicitly or implicitly. Once someone is considered a tenant, they are entitled to receive a notice to vacate, usually at least 30 days, before they can be legally required to leave. Additionally, most lease agreements have specific clauses that limit the duration a guest can stay without being added to the lease. If a tenant violates these terms by allowing a guest to overstay, the landlord may have grounds to terminate the lease and evict the tenant. Therefore, it is important for tenants to review their lease agreement and consult with an attorney before allowing someone to move in with them, especially if that stay becomes prolonged.