In 1889 William Morris Davis offered in his paper The Rivers and Valleys of Pennsylvania'' an elegant set of arguments for the origin of the ridges and gaps, and went on to propose a model for the drainage development and geomorphic evolution of the Appalachians. His work served to focus the geomorphic community into an intense, extended debate on the nature and fundamental controls of the long-term erosion of the Appalachians. The 100th anniversary of Davis' provocative paper prompted the convening of a symposium to address some of the fundamental questions about the Appalachians, the 1989 Geomorphology Symposium. The theme of this symposium was the geomorphic evolution of the Appalachians. This volume brings together a collection of papers from the symposium, to provide a summary of the current state of knowledge.