Neither practitioners nor academics in the field of public administration have agreed upon a satisfactory definition of administrative law. To help explain this present-day confusion, conceptual history of administrative law is presented. This history, which stresses how administrative law has been perceived, is divided into three major periods: 1893-1913, 1933-1946, and 1946 to the present. The definition is found to have began as the tripartite view of delegation of legislative authority, exercise of legislative authority, and judicial review, which later changed to a concern for the discretionary component of administrative law; the present-day definition includes substantive law. Because the New Deal era was critical in codifying administrative law and in setting the stage for the changes which followed, the New Deal and post New Deal years are examined closely. The work of Robert Jackson, who served as Solicitor General and then Attorney General under President Franklin Roosevelt, and then as Associate Justice of the Supreme Court from 1941 to his death in 1954, is used as the focal point for the examination. Jackson's work as government attorney had considerable impact on the field of administrative law, especially in his influence on the veto of the Walter Logan bill and the Attorney General's Committee on Administrative Procedure. His work as a Justice had less impact; most of his notable opinions are in dissent and have yet to be affirmed by the Court. The dissertation concludes with a discussion of Jackson's views of administrative law, the necessary components to a definition of administrative law, and the importance of accepting such components for methods of teaching public administration. / Ph. D.