Biological nitrogen fixation in grassAbstractNitrogen (N) due to their role in plant metabolism is the nutrient that most limits crop production. It ispresent in large quantities in air, primarily as di-nitrogen, but unfortunately the plants are not able to 8 Evidência, Joa aba v. 12 n. 1, p. 7-18, janeiro/junho 2012directly use the nutrient in that form, requiring it to be fixed in the form of ammonia. In soil, the fixed N isconverted to nitrate by nitrification process (mediated by Nitrossomonas sp. and Nitrobacter sp. bacteria),thus becomes available for plants. The N fixation may occur via atmospheric, biological and industrial, andthe last was and still is a pillar in the construction and maintenance of modern agriculture. The biologicalnitrogen fixation (BNF) provides economic and environmental advantages, being characterized asan important tool in achieving a more sustainable crop production. Plants of the family Fabaceae (legumes)has the efficiency in the process of BNF known and consecrated, however, four more crops produced inthe world (sugar cane, corn, rice and wheat) are of the family Poaceae (grass), and exploitation of BNF inplants of this family is a recent possibility, with relatively low efficiency, however, the optimization ofthese processes can bring significant benefits, since plants of this family are of paramount importance inproducing food, fiber and energy. Based on the above, this review summarizes knowledge regarding theprocess and efficiency of non-nodulating diazotrophs in Poaceae, in order to assess the state of the scienceof BNF this plants family.