Mushrooms are a tasty part of a modern diet and a valuable source of dietary protein. Every year Australians eat nearly 70,000 tons of button mushrooms (Agaricus bisporus), as well as smaller amounts of other fungal species such as oyster and shiitake. Button mushrooms are grown on a highly selective mushroom compost that is produced from recycled agricultural wastes (wheat straw and chicken manure). This controlled, industrial-scale microbial process is an accelerated version of the natural microbial decomposition of lignocelluloses, by which fungi and bacteria return nutrients from leaf litter to soils. The engineered process of mushroom composting includes a mesophilic wetting step, a thermophilic step and a mesophilic conditioning step, with each step characterized by a succession of typical microbial communities. The late thermophilic phase is dominated by Thermus, while the conditioning step is dominated by the ascomycete Mycothermus thermophilus. This fungus is associated with several specific bacterial species, including heterotrophic nitrifiers from the Pseudoxanthomonas and Chelatococcus genera. Their combined microbial biomass provides the initial food source for the Agaricus mycelium as it proliferates through the conditioned compost. Our work on the specific fungal and bacterial interactions that mediate mushroom composting aims to understand these interactions in detail, while also maximizing output and quality of the mushroom crop and addressing questions of nutrient retention, greenhouse gas release and water conservation.