LysM receptor-like kinases (LysM-RLKs) belong to the multi-gene family whose extracellular domains are directly involved in the perception of glycosyl compounds including chitin, peptidoglycans, and lipochitooligosaccharides, thereby activating pathways of plant immunity or symbiotic signal transduction. The function of the first LysM receptor gene, LYK3, in the model legume Medicago truncata was characterized in 2003. Subsequently, the function of more and more LysM receptor kinases was identified. This article provided a detailed enumeration and functional characterization of the LysM-RLK family in M. truncatula. The progress on studying LysM receptor kinase family in nodulation symbiosis, mycorrhizal symbiosis, and immune perception of Medicago truncata was summarized. It is indicated that the expansion of the number of LysM-RLKs genes within the M. truncatula has led to functional differentiation, but there is a phenomenon of functional redundancy among some genes as well. In addition, a close cross-linking between immune and symbiotic signals at the level of receptor perception mediated by LysM-RLKs was revealed. It will provide effective references and perspectives for further studying LysM-RLKs genes in M. truncatula.