Symbiotic nitrogen fixers are organisms that form a mutually beneficial relationship with plants by converting atmospheric nitrogen into a usable form for the plants. They are an essential component of healthy soil, and a cornerstone of sustainable agriculture. Some synonyms for symbiotic nitrogen fixer include nitrogen-fixing bacteria, legumes, diazotrophs, and rhizobia. Nitrogen-fixing bacteria are bacteria that live in the soil and produce nitrogen compounds that plants can use. Legumes are plants that have the ability to fix nitrogen in their roots by hosting nitrogen-fixing bacteria. Diazotrophs are microorganisms that can fix nitrogen in the soil, and rhizobia are a type of bacteria involved in symbiotic nitrogen fixation with legumes.