One of Davis's most significant contributions to geography was the development of the geographical cycle theory. This theory outlined a conceptual model for the evolution of landforms over geological time scales. According to Davis, landscapes undergo a series of stages, beginning with youthful stages characterized by high relief and vigorous erosion, followed by mature stages with more subdued relief and extensive erosion, and finally reaching old age with low relief and minimal erosion. This theory provided a framework for understanding the dynamic interactions between geological processes and landform evolution.

Davis's concept of "graded streams" revolutionized the understanding of river systems by proposing that streams adjust their profiles to achieve a state of equilibrium between erosion and deposition. He also introduced the idea of "base level," the theoretical limit to which a stream can erode, which has profound implications for landscape development and river behavior.

Furthermore, Davis's work on coastal morphology emphasized the role of processes such as wave action, longshore drift, and sea level change in shaping coastlines. His research laid the groundwork for understanding coastal erosion, sediment transport, and the formation of features such as beaches, spits, and barrier islands.