This book brings together sixteen chapters that present and discuss recent discoveries on soils and interactions between plants and soil organisms. The physico-chemical study of soils helps understand how some of their horizons promote the establishment of underground fauna (earthworms, springtails, mites...) and, consequently, how this creates new spaces that will be colonized by other soil organisms, especially microbes. The characterization of soil microorganisms through metagenomic approaches reveals that the presence and type of microbial populations depend on environmental conditions or types of crops. It facilitates the definition of bioindicators, which in this book are particularly illustrated on a national scale in France. Finally, molecular genetics studies show that plant root exudates are capable of shaping the root microbiome, inhibiting or activating the growth of specific microbial populations. Such scientific advances open up new avenues to guide plant-microorganism interactions. Raising awareness of the beneficial effects of soil microbes on plants will help establish more sustainable and resource-efficient cultivation systems. These research findings have enormous potential for the development of agroecology. This multidisciplinary book is intended for agronomists, students, and higher education teachers in agronomy, as well as any researcher interested in accessing the scientific foundations of eco-responsible agriculture.