What is the Halachic Function of a Written Lease?

Rav Baruch Meir Levin

Question: Typically, when someone rents a residential house or apartment, he has to sign a lease. What is the function of this lease? Is it necessary according to halacha to have one? 

Answer: A rental needs a kinyan to make it binding. There are three ways to make a kinyan on land: Kesef (money), shtar (a contract), or chazakah (moving in). Even if there is no written lease, the tenant will be making a kinyan once he moves into the property. Furthermore, there is a halachic rule of “kol t’nai sechirus ain tzorich kinyan”, which means that the spoken terms of a rental agreement are binding when one moves in, even without a written contract. 

Therefore, a written lease would only be necessary if it is meant to stop a tenant from backing out before he moves in. Once a tenant moves in, there is no real need for it. However, it is highly advisable to always write a lease because there may be misunderstandings or arguments about the terms later on. If everything is clearly spelled out in writing, that would solve most disagreements.