As one of the masterworks of modern American architecture, Philip Johnson's Glass House is a key monument in postwar construction. It is significant because it epitomizes the International Style and has long been regarded as one of the premier representatives of modernism. It also has national significance because of its association with Johnson, whose work as an architect and critic has had a profound effect on the course of 20th century architecture. Finally, the Glass House estate--including both the original 1949 elements and the subsequent additions made by Johnson--is significant because it provides an understanding of the architect that no other single property can equal. - NPS