Legumes represent the most-valued food after cereals for humans and animals. They are grown extensively in the dry/semiarid tropics worldwide, mostly under rainfed conditions. Legumes have the potential to establish symbiotic relationships with both rhizobial bacteria and arbuscular mycorrhizal fungi (AMF). This cooperation leads to atmospheric nitrogen fixation in nodules and phosphorus in arbuscules. Recent advances in high-throughput sequencing and other molecular technologies have provided opportunities to study the molecular basis of symbiosis in legumes. Several important components of the gene networks involved in legume symbiosis have been identified, including microRNAs (miRNAs), which have emerged as key players in gene expression, developmental processes, and stress in legumes. To date, a plethora of conserved and legume-specific miRNAs have been reported that are associated with symbiotic interactions by experimental and bioinformatic approaches. In this chapter, we combine data from published literature-especially genomic and deep sequencing data on miRNAs involved in symbiosis, biological nitrogen fixation, and phosphorus availability through nodules and arbuscules-to address the specificity functions of miRNA in establishing symbiosis in legumes. Furthermore, we highlight the interaction of the legume microbiome and miRNA in particular, establishing symbiosis for environmentally sustainable agriculture and increased global crop productivity. However, due to the complex nature of xxx, a concerted effort is required to fully understand the roles of miRNAs in the development of symbiosis in legumes.