When Germans rent an apartment, the landlord usually asks for a Mietkaution, a rental deposit. Section 551 of the Civil Code limits it to three times the monthly rent, without the operating costs. The tenant may pay a cash deposit in three equal monthly installments. The first is due at the start of the tenancy. The landlord must keep the money separate from his own assets, and the interest belongs to the tenant. The deposit protects the landlord, and the separate account protects the tenant’s money.