This chapter examines how river dynamics are related to the magnitude and frequency of channel-forming events. First, basic flood-frequency and flow-duration concepts are reviewed. Second, the classic equilibrium perspective on adjustment between flow and channel form is examined and related to magnitude–frequency concepts defining geomorphic work. The classic concepts of dominant discharge, bankfull discharge, effective discharge, and bankfull channel form are introduced and discussed. Third, event-based perspectives on river dynamics, including the concepts of geomorphic effectiveness and river sensitivity, are presented. Factors that influence the extent to which a particular fluvial system is sensitive or insensitive to individual hydrological events are explored, thereby providing the basis for equilibrium versus disequilibrium conceptions of channel change.