Mountains, hills, and lowlands are exposed to a wide range of processes that erode rocks and transport sediment to depositional basins. We use cosmogenic nuclides to quantify these processes and to quantify their dependence on climate, tectonics, and land use, for example. We are particularly interested in mountainous regions, which account for a large fraction of all globally eroded material, and where erosion is thought to be very sensitive to climate change. We focus on the way glaciers shape mountain valleys, on the relationship to mountain uplift, and trace erosion back through the Quaternary past using cosmogenic nuclides in buried sediment.