The American frontier is sharply distinguished from the European frontier--a fortified boundary line running through dense populations. The most significant thing about the American frontier is, that it lies at the hither edge of free land. In the census reports it is treated as the margin of that settlement which has a density of two or more to the square mile. The term is an elastic one, and for our purposes does not need sharp definition. We shall consider the whole frontier belt, including the Indian country and outer margin of the "settled area," of the census reports. This paper will make no attempt to treat the subject exhaustively; its aim is simply to call attention to the frontier as a fertile field for investigation, and to suggest some of the problems which arise in connection with it.... The stubborn American environment is there with its imperious summons to accept its conditions; the inherited ways of doing things are also there; and yet, in spite of environment, and in spite of custom, each frontier did indeed furnish a new field of opportunity, a gate of escape from the bondage of the past; and freshness, and confidence, and scorn of older society, impatience of its restraints and its ideas, and indifference to its lessons, have accompanied the frontier. What the Mediterranean Sea was to the Greeks, breaking the bond of custom, offering new experiences, calling out new institutions and activities, that, and more, the ever retreating frontier has been to the United States directly, and to the nations of Europe more remotely. And now, four centuries from the discovery of America, at the end of a hundred years of life under the Constitution, the frontier has gone, and with its going has closed the first period of American history. PAUL SAMUEL REINSCH Professor Reinsch was born in Milwaukee in 1869. He received his A. B. from the University of Wisconsin in 1892 and his doctorate in 1898. He had the advantage of studying at the University of Berlin and at Rome and Paris. He was assistant professor of political science at his Alma Mater from 1899 to 1901, and full professor from 1901 to 1913, except for two years, 1911 and 1912, when he held the Roosevelt professorship at the Universities of Berlin and Leipzig. Since 1913, he has been Envoy Extraordinary and Minister Plenipotentiary to China. His present address is the American Legation, Peking, China.