In soil, plants are exposed to harmful microbes that give disease (pathogens) and beneficial microbes that promote plant health. Interestingly, plants can perceive and respond to odours produced by microbes before contact. In my PhD thesis, I studied the chemical composition of odours emitted by pathogenic and non-pathogenic fungi in soil, and I studied the effects of these odours on plant development and resistance. I showed that odours from fungi, irrespective of their pathogenicity, can positively affect plant growth and accelerate flowering. Additionally, exposure of plant roots to these odours influenced subsequent plant interactions with herbivores, making sometimes plants more resistant to herbivores feeding on roots or leaves. Together, the findings of this study provide fundamental information on plant-fungus interactions, and highlight the ecological importance of such interactions for plant health. In the quest for sustainable agricultural practices, odours from soil microbes represent promising candidates for crop protection and stimulation.