Explain what is meant by an implied warranty of habitability and how this doctrine has changed the common law approach with respect to residential leases

Under the common law, the landlord is under no obligation to provide or maintain the premises in a livable condition unless the lease so provides. Most courts have abandoned this common law rule. The implied warranty of habitability requires leased premises to be habitable and fit for ordinary residential purposes. The covenant to pay rent is conditioned on the landlord's performance of this warranty. The emphasis by the courts in residential leases is that the tenant's interest is in a place to live, not merely in the land. A number of states have statutes requiring landlords to keep residential premises fit for occupation. Zoning ordinances, health and safety regulations, and building and housing codes may also impose certain duties upon the landlord.