The use of benefits estimates in environmental decision making has received increased attention in the United States over the past two decades. Environmental benefits have been estimated for a number of purposes, and major strides have been made in the theory and practice of environmental benefits assessment. For example, "Environmental Impact Statements" (EIS) are required for many construction projects and other activities, and much of the early development of benefits measurement methodologies involved the evaluation of individual projects. Since the early 1970s, the use of some type of formal benefit-cost and economic impact analyses has been required to support Federal environmental regulations. Environmental benefits estimates have also been developed as part of more general policy studies.