Rental contract / lease (Mietvertrag).
Contract between tenant and landlord, typically in writing and fixed-term or open-ended.
The rental contract is the legal basis of the lease. Swiss law does not require written form, but in practice every lease is written.
Minimum content: - Parties (landlord, tenant) - Property (address, rooms, m²) - Rent (net), utilities - Lease term (fixed/open-ended) - Termination conditions - Security deposit - Handover condition
Fixed vs. open-ended: a fixed-term contract (e.g. 1 year) ends automatically. An open-ended contract runs until terminated and is the more common form in Switzerland.
Before you sign: don't sign anything you don't understand. When in doubt, consult the Mieterverband (membership from CHF 75/year). aptari helps you find the flat and apply; the lease itself is signed directly with the landlord or agency.