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The concept that erosion, over a long period of time, would produce an evolutionary progression of landforms culminating in a nearly flat plain, the peneplain, was formulated into a coherent theory by W. M. Davis. Subsequent to early identification of the Fall Zone (oldest), Schooley, Harrisburg, and Somerville (youngest) peneplains, numerous workers pursued identification, correlation, description, folding, formative processes, and dating of Appalachian peneplains for 6 decades. Following a peak of interest and activity in the 1930's, work on Appalachian peneplains declined rapidly. Reasons for the decline include: death of former workers, diversion into other lines of research, and rise of process geomorphology. Phenomena attributed to a dependence on peneplanation include: origin of present drainage, origin of some mineral resources, and cementation of rock units. Attacks on the peneplain idea have been largely unsuccessful except for the dynamic equilibrium concept advocated by John Hack. Controversy exists about whether the disparity between rates of uplift and denundation allow adequate time for peneplanation to occur. The relationship of some surficial deposits to presumed peneplain surfaces is problematical. The peneplain concept is still alive, but new lines of research are required to resolve its controversial position.