Landforms created by running water dominate the land surface of earth. However, although the role of water is seen everywhere, it is seen at its best in those regions where the climates are wet enough to support a forest vegetation with a continuous canopy. The seasonal fluctuations in the character of precipitation with snow in winter and rain in summer which characterize cool temperate forest climates and the legacies of recent past cold periods in high latitudes means that the landforms of the humid tropics should be regarded as the "normal" or "type" features due to erosion by running water. This discussion of humid landforms, together with J. A. Mabbutt's volume Desert Landformscompletes a series of seven volumes on systematic geomorphology. It attempts to break with traditional approaches and to discuss humid landforms from the standpoint of the humid tropics. In addition, it seeks to demonstrate that the processes creating and destroying landforms are also those that regulate biotic activity at the earth's surface. The approach followed in this book is to describe the processes affecting the evolution of landforms in terms of the circulations of energy, water and materials before introducing the complication of legacies of different ages from the past. Theories of landform evolution are briefly reviewed in the final chapter.