Microbes play a key role in ecosystems. Many microbes are beneficial to plants and ecosystems. It is, thus, of utmost interest to understand which factors determine microbiome composition and to assess whether it is possible to engineer the microbiome for promoting soil, plant and environmental health. In recent years, we have been testing whether it is possible to engineer the microbiome in agricultural fields. We performed large scale field inoculations with arbuscular mycorrhizal fungi (AMF), a group of beneficial soil fungi that can improve plant nutrient uptake. We observed that field inoculation with AMF can promote plant yield (significant yield increases of up to +40% were detected). AMF inoculation was especially successful in fields where pathogenic fungi were present indicating that AMF enhanced soil health. We further observed that the beneficial impact of AMF on plants is linked to hyphal associated bacteria and a range of observations indicate that in fact a tripartite mutualistic association between plants, fungi and bacteria drives the success of the mycorrhizal symbiosis. Microbiome engineering is also possible by altering agricultural management, including altering crop rotation, pesticide use or land use. Overall, this talk highlights that soil microbes are an integral part of One Health.