This paper reviews the role of market failures in land markets, evidence as to their quantitative significance and the impact of land use policies designed to offset for such failures. Policies of containment and densification limit the supply of land for all urban uses. When applied as stringently as in Britain, a full net welfare evaluation shows the increased costs of space for housing substantially exceed the value of amenities generated. There is also evidence that constraints on land supply impose costs on productive uses of land in both office and retail use. Although the estimates are that these costs are considerable they relate only to the gross costs. Three possible policy changes are identified which could preserve the role of regulation in offsetting for problems of market failure while greatly relieving the costs of policy-imposed supply restrictions.