Termination protection
Landlords can't just terminate. Legitimate reasons: Personal use (moving in themselves), serious contract violations, economic utilization. Formal errors invalidate terminations. Notice periods: 3-9 months depending on tenancy length.
Rent increases
Your landlord can't raise rent arbitrarily. Maximum to local comparable rent (Mietspiegel), maximum 20% in 3 years (15% in cities with rent cap). Graduated and index rent are exceptions. Increases must be justified.
Defects and repairs
Landlord is responsible for maintenance. Report defects in writing, set deadline. For major defects (heating broken, mold) you may reduce rent. Small repairs clause: Usually up to €100 per repair, max €200/year.
Deposit
Maximum 3 months cold rent. Must be kept in separate account. Can be paid in 3 monthly installments. Return after move-out: Landlord has 3-6 months for settlement. No offsetting with disputed claims.
Rent cap (Mietpreisbremse)
In tight markets, new rent can't exceed previous rent by more than 10% above local average. Exceptions: New construction, extensive renovation, furnished apartments. You can reclaim overpaid rent - but only if you object.