Sebacinales have emerged as a fascinating order with mutualistic plant-fungal symbionts that consists of exclusively beneficial fungi. This volume of Soil Biology presents an overview of the current results in Sebacinales research with a focus on the potential of these fungi in crop improvement and stress tolerance. The authors demonstrate that Sebacinales are not only extremely versatile in their associations with roots, but are also almost universally present as symptomless endophytes. With this extraordinary diversity, Sebacinales with the key fungus Piriformospora indica might possess remarkable significance in natural ecosystems. Their biotechnological applications are expected to improve the quality of crops while maintaining ecologically and economically sustainable