A rental agreement is a document that acts as a contract between you and your tenant, defining the terms of the tenancy. You can have it written in a way that is favorable to you because you can decide what goes into the agreement. Most rental agreements are short-term agreements, such as month-to-month tenancies, while lease agreements are usually for longer rental periods, such as six months, a year, or more. A rental agreement is a good idea if you want to make sure your tenant is reliable or if you're renting a room in a house in which you're living. It's easier to terminate a month-to-month tenancy than a long lease.