We all know the important role our forests and grasslands play in keeping our planet livable and wonderful. But scientists are only now beginning to understand the degree to which all these plants are supported by huge underground networks of fungi that have formed a symbiotic relationship with the plants' root systems. As we learn more about where these fungal structures are and how they work, we can find ways to protect them, which will in turn protect the entire ecosystems of plants and animals above them.