Diazotrophs are a dominant source of newly fixed nitrogen in many ecosystems.  Most research has concentrated on the symbiotic relationship between plants and nodule-inhabiting bacteria (e.g., Rhizobia).  However, diazotrophs contribute significant amounts of nitrogen to a myriad of lesser-known ecosystems.  They can be endoliths, hypoliths or occur in aquatic habitats in any climatic zone. In deserts and polar regions, they cover many surfaces, including soils, rocks, mosses, lichens, and live and dead plant stems, root, and leaves. In boreal forests, they are on and in mosses that carpet the forest floor. In coniferous forests, they occur on and in lichens colonizing tree branches. In temperate regions, they associate with the non-vascular plants commonly found on the soil or plant litter surface.  Diazotrophs are found in peatlands and mires. In the subtropics and tropics, they are on terrestrial and intertidal tree and grass stems, roots, and leaves. They occur in hypersaline lakes and thermal hot springs. The newly-discovered picoplankton are dominated by cyanobacteria (e.g., Prochlorococcus, Synechococcus) and thus are likely a huge source of N in oceans. Diazotrophs are found associated with various carnivorous plants and are in the air. They live symbiotically with animals such as corals, polar bear hairs, and sea hares.  They are found in the stomachs of termites, pigs, guinea pigs, and humans. We will estimate nitrogen inputs from these obscure sources and compare these numbers to current estimates of nitrogen inputs from more well-known sources.