If you rent a property without a written lease, you are a tenant at will. You have several protected rights as guaranteed for all renters by your state laws. Having no lease also may benefit you in certain situations. Your status as a tenant at will generally affects the length of notice required for various actions.
You don't need a written lease to rent a property and retain common renter's rights. You have an implied lease based on your oral agreement with your landlord. The length of the lease is usually at least as long as the period between your rent payments. For example, if you pay your landlord every month, then you have an implied month-to-month lease.
If you want to move out, you can do so by giving your landlord notice that is at least as long as the lease period. The notice period should end on the day you usually pay rent. For a month-to-month lease, this means that you have to tell your landlord that you want to move out on the day you pay your last rent, one month before you actually vacate the property. You don't have to pay any penalty because you don't have a lease.
When you move into the rental property, you may be required to pay the landlord a security deposit in case you damage anything in the property. Your landlord has to give you back your security deposit, minus any deductions, within a certain period of time after you move out and return the keys. Depending on your state laws, this time period may be shorter for a tenant at will. In Maine, for example, the limit is 21 days for a tenant at will and 30 days for a tenant with a lease.
Your state laws determine the terms under which your landlord can evict you. Your landlord usually has to give a notice of at least 30 days before the day you are expected to leave. Your landlord may not have to give you any reason for evicting you. If you fail to pay your rent or have seriously damaged the property, your landlord may be able to give you less than 30 days' notice for eviction.