Aim: To understand the effects of climate change and extreme events on river ecosystems. Main concepts covered: This chapter focuses on the key areas in which climate change will affect and already is affecting river ecosystems. These include species range shifts, reorganization and invasion; complex and nonlinear population, community and ecosystem responses; coupled geomorphological-ecological linkages; interactive responses with other stressors; altered flow regimes, and how these changes link with species adaptations to natural flow regimes; and thresholds and regime shifts in response to change. Conclusion/Outlook: Climate change is altering river flow and thermal regimes globally, including altering the magnitude and frequency of extreme events, and this is already having a major detrimental effect on river ecosystems. These effects are set to continue and potentially accelerate as the climate continues to change. I offer a few solutions to minimize the detrimental effects of these changes.