Gravitational forces applied to water masses on sloping surfaces drive the currents in fluvial systems. These currents as a rule develop in alluvial deposits composing the river channel and hence interact with deformable channel boundaries – the river bed and banks. Erosion and deposition of alluvium within a river channel and its valley result in a variety of forms that in turn create specific patterns of river currents. The content of this chapter is restricted to the most fundamental types of currents: river flows in a straight river reach, modifications of the current due to channel curvature, flows at river confluences, currents that develop near engineering structures, and currents induced by commercial navigation. Although these basic types of flows are more or less understood individually, their superposition in natural streams is still difficult to understand and predict quantitatively. Therefore, studies of river flows always require experimental and field methods. In this article the currents are discussed using, where possible, the theoretical frameworks provided by modern fluvial hydraulics and geomorphology, and illustrated by the results of original field investigations completed by the authors.