In this paper the processes of erosion at the watershed management which operate on the banks of river channels are outlined briefly in order to illustrate the importance of one particular process to bank stability. This process is the fluvial entrainment of bed and bank material from the watershed area. Processes of erosion on river banks fall into two major categories: fluvial entrainment, and weakening and weathering during the watershed management. Fluvial processes are associated with the hydraulics of flow in the channel whilst weakening and weathering of the bank material are controlled by climatic conditions at the watershed management. These processes act independently to erode a bank. The mechanics of failure of a bank are related not only to the nature of the forces of erosion but also to the size, geometry and structure of the bank and the engineering properties of the bank material. Banks may be classified on this basis as non-cohesive, cohesive or composite and by size and geometry within these broad classes. The interaction of motive and resistive forces in determining bank stability is considered and methods of stability analysis are presented at this research. The implications for bank protection, width adjustment and rivershed management effects are discussed.