Population growth has been traditionally regarded with some satisfaction in the United States, being associated with economic and social benefits and rising standards of living. Population expansion has, inter alia, provided an increasing labour force, larger and more varied markets and a widening range of opportunity for individuals. By 1967, however, as the U.S. population officially passed the 200 million mark, reactions were becoming decidedly ambivalent. Expressions of pride and pleasure, and the anticipation of further economic growth were somewhat soured by the widely publicized views of conservationists and ‘environmentalists’ (a rather newer breed). The old attitude of mind in fact paid little heed to the problems accompanying large population expansion and rapid changes both in patterns of living and in geographical distribution. In the late 1950s and early 1960s, however, concern about these matters began to grow, and the assumed arrival of the 200 millionth American heralded a sizeable campaign concerned with the threat, so called, of ‘over-population’. Stewart Udall, then Secretary of the Interior, writing a Foreword to his Department's report ‘The Population Challenge’, stated flatly ‘The greatest threat to quality of living in this country is overpopulation’. He spoke of the challenge of a soaring population; the shrinking amount of space per head; the gathering storm of conflict on space allocation, on resource utilization and on the preservation of the quality of environment. The headings of various sections of that report – ‘A Rationed Tomorrow’; ‘So Much and No More’; ‘Planning for the Pinch’ – all reflect urgent concern about the size and rate of growth of U.S. population with its growing pressure on land and other resources.