Rent control is a government regulation giving tax incentives for landlords who abstain from increasing rent beyond a certain amount. The "control" expires when the tenant leaves, which means that in taking the tax incentive, landlords make a calculated gamble - will the benefit of the tax incentive outweigh the lost revenue of the tenant's decreased rent? Often the "gamble" pays off for the landlord, but has been known to lead to very low results, such as an apartment for $500 per month in New York's Upper East Side.
Some argue that rent control causes a shortage in housing because it removes the incentive for landlords to incur costs to build or renovate new units. To address such a shortage, sometimes rent control will not apply to new units.