This chapter provides an overview of most of the main sources and pathways of both sediment and contaminants in river systems, describes sediment–contaminant transport processes in rivers, and examines some of the main natural and anthropogenic perturbations to these sources, pathways, and transport processes. This information provides an understanding of the sediment–contaminant system so as to effectively target management and to mitigate the detrimental impacts (whether real or perceived) of sediment–contaminant dynamics in river basins. Furthermore, it allows assessing the responses of the sediment–contaminant system to any interventions, whether they be site-specific or basin scale. Such information, therefore, represents an important requirement for sediment management frameworks and plans. The task of obtaining a complete understanding of sediment–contaminant sources, pathways, and transport processes at the river basin scale probably represents one of the greatest challenges facing those concerned with sediment management.