In U.S. law, the term "public private partnership" is a term that began to be used in the late 1990s and early 2000s in two distinct but related senses. In both cases, the term is used to denote government contracts in which the private contractor takes on more responsibility than has been customary in the past for the delivery of the services contracted for. With respect to transportation infrastructure, such as highways and bridges, the term refers to a family of relatively new contract types, actively promoted by the federal government for use by state governments, such as Operations and Maintenance or Design-Build-Finance-Operate-Maintain, by which the government is able to shift much of the financing, maintenance, and/or operating cost for public infrastructure to private contractors, who may then be allowed to recoup their costs through tolls or other user payments, thus enabling the government to use the market to accomplish its purposes and to relieve public budgets of the financial burden associated with infrastructure upgrading and maintenance. By extension, the term has been applied broadly to all types of contracting out of important government services, including such things as schools and prisons, provision of health care, and even the administration of state welfare programs and financial rescue of the economy. In neither case are the contract types in question really new. There is an extensive history of such use of government contracting, both with respect to transportation infrastructure and more broadly. But the use of the term "public private partnerships" appears to symbolize a new enthusiasm for privatizing governmental functions. In both cases, this extensive use of contracting out raises important public law questions, both with respect to the ways in which the enthusiasm for contracting out has led to efforts to weaken existing legal protections for the public interest and with respect to the ways in which existing law fails to ensure that public values and interests are protected in such contracting out.