Beijerinckiaceae is a family of nitrogen-fixing bacteria within the order Rhizobiales. These bacteria are gram-negative, motile rods that can exist as free-living organisms in soil or as symbionts in root nodules of leguminous plants. They play a crucial role in the global nitrogen cycle by converting atmospheric nitrogen into ammonia, which is a form of nitrogen that plants can use for growth. Some notable genera within this family include Azorhizobium, Beijerinckia, and Methylocella.