Cell-cell communication or quorum sensing (QS), a common way of regulating phenotypes at the population level, relies on the self-production of small molecules accumulating extracellularly along growth. In Gram-negative bacteria, the main signaling compounds belong to the N-acyl-homoserine lactone (AHL) family and are synthesized by an AHL synthase (LuxI family) and recognized by a transcriptional regulator (LuxR family) that triggers the expression of specific genes. This chapter presents the initial studies of QS that was focused on 40 strains of Azospirillum and revealed that only 4 strains isolated from rice were able to synthesize AHLs. A genome mining for QS genes conducted on 43 Azospirillum genomes (from 24 validated species) highlights the presence of a complete QS system in only 5 genomes from species belonging to the lipoferum clade, while a strain possesses only a luxI gene and 12 strains bear orphan luxR genes. The potential to interfere with quorum sensing, i.e., quorum quenching, is also surveyed and seems to be widespread, although functional evidence is needed. Finally, methodology for AHL extraction and characterization, as well as for identification of genes mediating AHL-based QS and QS-controlled functions, is provided.