Legumes are important components of the nitrogen cycle on land. Agricultural systems have traditionally relied much on legumes for nitrogen input because many species are able to establish symbioses with diazotrophic bacteria (rhizobia) and thus trade metabolites and reduced compounds. Photosynthates produced in the leaves are allocated to the root nodule to supply the bacteroids with carbon, in exchange for reduced nitrogen (ammonia) produced by the rhizobia from atmospheric nitrogen. Despite its major significance to plant breeding and sustainable agriculture, the impact of abiotic stresses on nodule development and stability and on symbiotic nitrogen fixation remains poorly understood, particularly at the molecular level. However, the study of model legume species and the development of a plethora of resources, particularly the elucidation of the genome sequences of three legume species, are now revealing many traits of agricultural importance in legumes as well as other aspects that are not easily studied in other plant models, such as Arabidopsis or rice. In this chapter, we will discuss the effects of abiotic stresses, such as drought, phosphate deficiency and aluminium toxicity, on symbiotic nitrogen fixation and provide perspectives on molecular approaches to the analysis of stress responses in legumes.