Plants are an intrinsic part of the soil community, which is comprised of a diverse range of organisms that interact in the rhizosphere through continuous molecular communications. The plant-microbe continuum forms a network of underground nutrient and information highways that benefit both plant and microbial communities, as well as ultimately serve as a significant sink for atmospheric CO ₂. The molecular dialogue at the rhizosphere interface is crucial not only for plants to discriminate between harmful, benign, and beneficial microorganisms but also to actively participate in crop productivity and resilience to environmental stresses. Although many facets of the chemistry of inter-organism communication remain to be discovered, and the molecular mechanisms that underly hormone-regulated symbiosis are largely unexplored, biological fertilization is an attractive tool for the sustainable production of high-value crops. Here, we discuss our increasing knowledge of the chemical repertoire that underpins plant-microbe communication and host-range specificity, highlighting how the regulated production of reactive oxygen species (ROS) is used in inter-organism communication between plants and microbes and within the communities that shape the soil microbiome.