All plants studied in natural ecosystems are symbiotic with fungi that either reside entirely (endophytes) or partially (mycorrhizae) within plants. These symbioses appear to adapt to biotic and abiotic stresses and may be responsible for the survival of both plant hosts and fungal symbionts in high stress habitats. Here we describe the role of symbiotic fungi in plant stress tolerance and present a strategy based on adaptive symbiosis to potentially mitigate the impacts of global change on plant communities.