The rent control cap was introduced in Germany in 2015 and applies in areas designated by state governments as tight housing markets. Landlords may not increase rents by more than 10% above the local comparative rent when re-letting properties. Exemptions apply to new buildings first rented after October 1, 2014, and extensively modernized apartments. Tenants can challenge excessive rents and demand repayment of overpaid amounts. The effectiveness of this instrument is debated among experts, as numerous exceptions significantly limit its scope, and it does not directly increase the supply of rental housing. Similar rent regulation concepts exist in many European countries, though their specific design and enforcement vary considerably.