This chapter focuses on the different roles of ectomycorrhizalmycorrhizaectomycorrhiza fungiectomycorrhizal fungi, and thereby mostly mushroom-forming basidiomycetesbasidiomycete and their importance for agroforestryagroforestry or afforestationafforestation in times of climate change. To reduce carbon dioxide emissions, production of lignocellulose would be an option. However, the question of fuel over food poses a serious problem that needs to be considered carefully. Therefore, the use of degraded land, e.g., with high metal loads resulting from mining activities, could provide a solution, given growth of trees could be supported without further increasing agrochemical use. Here, ectomycorrhizalmycorrhizaectomycorrhiza fungi might provide a solution. The same holds true for afforestation programs that consider future more serious droughts, as mycorrhiza can redistribute water in the entire forest ecosystem. To understand these ecosystem functions of mycorrhizal fungimycorrhizal fungi, the impact on the soil properties, on the bacterial community composition and on the host are revisited. Ectomycorrhizae tend to be host specific, which involves early signaling through volatile organic compounds, specifically terpenes, as well as production of phytohormones and their influence on the host tree. In planta, the mutually symbiotic relationship involves the formation of highly branched mycelia between plant root cells, the Hartig’ netHartig’ net, which is discussed with respect of cell wall covering fungal hydrophobinshydrophobin. Taken together, the molecular biology of the ectomycorrhizalmycorrhizaectomycorrhiza fungi can explain for which applications in agroforestry these association may be helpful—including the use of degraded land.