This chapter reviews fundamental fluvial processes and concepts to provide a basis for subsequent chapters oriented toward understanding environmental impacts of lowland river management. The goal of this chapter is to review relevant fluvial processes from a drainage basin perspective, including headwater, transfer, and deposition zones. Human impacts across headwater landscapes, especially improper agricultural and mining practices, causes upstream land degradation that can drive downstream fluvial adjustment with adverse consequences to riparian environments. Several regional land degradation case studies are briefly introduced to provide a link with downstream impacts. Characteristics of alluvial river channel patterns are reviewed to afford a perspective for considering several modes of fluvial adjustment to upstream impacts and hydraulic engineering of lowland rivers, which provides a segue to Chapter 3.