It is a legally binding document between you and the landlord, applicable only to you and the property you are renting, which states the amount of rent, the length of the tenancy, your rights and responsibilities. Your agreement will most probably be an Assured or an Assured Shorthold tenancy under the Housing Act 1988. However, for company lets and/or rental values over £25,000 a year, the agreement will be drawn up under contract law.