An interaction between Legumes and Rhizobia establishes a symbiotic new organ, the nodule that supports atmospheric nitrogen fixation. The specific communications between the microbes and legume plants are necessary for both nodulation and nitrogen fixation. Through genetic and biochemical analyses several genes playing pivotal roles in nodulation had been identified to be a receptor kinase like CALVATA1 involved signal transduction for development. This emphasizes peptides as signals to be transmitted for a short or long distance transport for nodulation. In addition, a quorum sensing in rhizobia has become a focus as counterpart signal. In an attempt to reveal proteins factors and signaling molecules acting on nodulation, proteome analyses of nodule and the proteins in apoplast upon communication between Legumes and Rhizobia were performed.