What is a legal nonconforming use?

A legal nonconforming use exists when a property's use was permitted under the zoning in effect when it began, but a later change in the zoning ordinance no longer allows that use. Rather than forcing immediate removal, zoning law generally lets the use continue as 'grandfathered,' though typically with limits — the owner usually cannot expand it, rebuild it if destroyed, or resume it after it has been abandoned. This differs from a variance (permission to deviate from current zoning) and a conditional use permit (a use allowed in a zone if specific conditions are met). The concept frequently appears in land-use questions on the national exam.