Contemporary authors' definitions of supervision suggest that in the American public school supervision evolved from four major conceptual foundations: (1) human concern, (2) leadership, (3) instructional improvement, and (4) administration. The categorization of definitions and explanations from 21 leading supervision authorities of the past 50 years is presented in a table. An analysis of these definitions reveals that, of the 21 authors, 19 perceive instructional improvement to be the cornerstone of supervision; 17 also express the necessity of leadership in supervision; and 13 state the relationship between supervision and administration. However, only 12 of the 21 authors stressed the human concern "foundation" of supervision. This lack of emphasis on human concern can be directly related to the scientific and rational approach to supervision. Philosophically, however, most of the authors cited would agree that supervision must be concerned with the human element in both students and teachers. (MLF)