Medicago truncatula (barrel medic) is a species native to the Mediterranean that has been adopted as a model organism for temperate legumes due to its relatively small size, short generation time, small diploid genome and the capacity to reproduce by self- and out-crossing. It is a close relative of alfalfa (M. sativa), which is used as forage, but it is also a model organism for other legume crops used for human consumption such as pea (Pisum sativum), lentil (Lens culinaris) and faba bean (Vicia faba). As many other legumes, M. truncatula establishes a nitrogen fixing symbiosis with soil bacteria called Rhizobia, which accounts for a significant proportion of the nitrogen incorporated into the ecosystems. In addition, it has the capacity to interact with fungi to form mycorrhiza, an ancient root endosymbiosis important for plant mineral nutrition. In the past decade, a significant amount of genetic and molecular tools has been developed to study the biology of this model species: the sequencing of nearly its complete genome, the generation of genome-wide expression datasets, the development of techniques for stable and hairy root transformation, and the establishment of mutant collections for genetic studies. This compendium of tools allowed the dissection of the genetic networks that govern symbiotic association with bacteria and fungi. The knowledge generated in this model legume is crucial to improve crop productivity in agriculture.