The seafloor is one of the critical controls on the ocean’s general circulation. Its influence comes through a variety of mechanisms including the contribution of mixing in the ocean’s interior through the generation of internal waves created by currents flowing over rough topography. The influence of topographic roughness on the ocean’s general circulation occurs through a series of connected processes. First, internal waves are generated by currents and tides flowing over topographic features in the presence of stratification. Some portion of these waves is sufficiently nonlinear that they immediately break creating locally enhanced vertical mixing. The majority of the internal waves radiate away from the source regions, and likely contribute to the background mixing observed in the ocean interior. The enhancement of vertical mixing over regions of rough topography has important implications for the abyssal stratification and circulation. These in turn have implications for the storage and transport of energy in the climate system, and ultimately the response of the climate system to natural and anthropogenic forcing. Finally, mixing of the stratified ocean leads to changes in sea level; these changes need to be considered when predicting future sea level.