In work presented in 1883 and published in full in 1894, W.J. McGee made one of the first clear attempts to outline the main morphologic differences between glaciated valleys and valleys developed by processes dominant in more temperate areas. Moreover, with an unprecedented analysis of glacial erosion, he attempted for the first time to explain the evolution of glacial land forms in terms of theoretical predictions of patterns of erosion under valley glaciers. In the latter half of the nineteenth century, there was fierce debate over whether glaciers were even capable of significant erosion, so it is perhaps not surprising that McGee’s analysis of glacial erosion processes and land-form development received little attention in his own time. Despite this, McGee’s work provided some of the first really convincing glacial explanations for the development of land forms such as hanging valleys and U-shaped valleys, and these were developed more fully in later work by Davis (1900) and Gilbert (1903). In modern research, the use of theoretical erosion laws and a knowledge of ice dynamics to develop models of land-form development is emerging as a major theme in glacial geomorphology, marking a return to the methodology pioneered by W.J. McGee.