This chapter reviews the main features and large- to mesoscale mechanisms that contribute to the Amazon’s climate, its inter-annual and inter-decadal variability, and extreme drought and flood events. It examines the effects of extreme events on vegetation and the partitioning of precipitation into evapotranspiration (ET), runoff, flow seasonality, and floodplain dynamics; and describes the floodplain´s role in the biogeochemical cycle.