Signaling studies in the rhizosphere have focused on close interactions between plants and symbiotic microorganisms. However, this focus is likely to expand to other microorganisms because the rhizomicrobiome is important for plant health and is able to influence the structure of the microbial community. We discuss here the shaping of the rhizomicrobiome and define which aspects can be considered signaling. We divide signaling in the rhizosphere into three categories: (i) between microbes, (ii) from plants to microorganisms, and (iii) from microorganisms to plants. Signals act on diverse organisms including the plant. Mycorrhizal and rhizobial interkingdom signaling has revealed its pivotal role in establishing associations, and the recent discovery of signaling with non-symbiotic microorganisms indicates the important role of communication in shaping the rhizomicrobiome.