Technical Abstract: This chapter reviews some of the key concerns and challenges associated with dryland desertification, emphasizing the role of hydrological processes. Hydrological processes are a function of complex interactions and linkages between specific patch types and landscape units; and thus, one of the keys to understanding both the causes and consequences of land degradation. Degradation involves a reduction in the ability of the land to support one or more functions. The interpretation of change as "loss" is dependent upon the context of the socioeconomic activities of human beings. The chapter ends with a discussion of future directions, including the development of the Dahlem Desertification Paradigm (DDP), a new approach to desertification designed to facilitate directed research effort and progress.