This monograph is a fundamental study of watershed erosion and runoff processes. It utilizes decades of soil erosion data to take a comprehensive and balanced approach in covering various watershed erosion processes. While there are many works on soil erosion and conservation, this book fills the gaps in previously published research by focusing more on mass movement, gully erosion, soil piping/tunnel erosion, and the spatial interactions of different erosion processes. Additionally, the book examines erosion processes in extreme rainfall events, something typically absent in short-term studies but discussed in detail here as the book draws on 60 years of research and observations, including 30 years of the author's own investigations of erosion under a wide range of rainfall conditions. The book is divided into 3 parts, and is intended for soil erosion researchers and practitioners, and postgraduate students studying soil erosion and water conservation. Part 1 opens with a comprehensive and critical review of existing literature on soil erosion processes, discusses this book's place among existing literature, and examines the major erosion processes (rainwash, gully erosion, tunnel erosion, and mass movements) including their controlling factors and mechanisms. Part 2 explores the spatial interactions of these different erosion processes to provide a prerequisite for effective design of comprehensive soil erosion control measures in a watershed. Part 3 evaluates the relative significance of these erosion processes in sediment production, the effectiveness of comprehensive soil and water conservation programs, and the applications of watershed modelling in determining the impact of land-use changes on soil erosion and other ecological processes.