Nitrogen fixation is the primary natural source of new nitrogen in ecosystems. This new nitrogen can fuel productivity and sustain carbon storage, but it can also cause nitrogen saturation, potentially exacerbating environmental issues such as eutrophication and greenhouse warming. How the diverse groups of plants and bacteria involved in nitrogen fixation respond to environmental change, then, has major implications for biodiversity and ecosystem functioning. Indeed, recent modeling efforts indicate that the dynamics of nitrogen fixation are integral to forecasting global carbon dynamics, suggesting that a better understanding of nitrogen fixation will greatly improve our predictions of global climate change. In addition to driving environmental issues, nitrogen fixation also responds to anthropogenic environmental changes, creating feedback loops. Recent work has made great inroads into resolving some of the key questions concerning terrestrial nitrogen fixation. Much of this recent work has focused on four topics: the roles of (1) biodiversity and traits that are evolutionarily linked to nitrogen fixation; of (2) elements such as carbon, nitrogen, phosphorus, and molybdenum; of (3) global environmental change; and of (4) the dynamics of the symbiotic interaction between nitrogen-fixing bacteria and their plant hosts. This session brings together some of the leaders of these recent efforts, with expertise ranging from ecosystem science to physiology to the evolutionary dynamics of symbioses, and across a range of ecosystem types. This wide range of perspectives on nitrogen fixation showcases the broad spectrum of research focused on linking the nitrogen inputs from fixation to the biodiversity and ecosystem functioning that both respond to and help determine future global environmental change.