Although a multitude of fungi from the phylum Neocallimastigomycota has been around for ages and co-evolved with their herbivorous hosts, they have quite nicely evaded discovery by appearing as motile cells very similar to zooflagellates. It was quite a surprise when chitin in their cell walls unmistakably identified these microorganisms as fungi. They have been identified as common players in the digestive tracts of a multitude of different herbivores (both ruminant and non-ruminant mammals and even reptiles). This came as a surprise since until then their microbiome was thought to consist only of bacteria, archaea and protozoa. Due to their widespread presence in all kinds of herbivores it became clear that they play an essential role in the digestion of fibre-based plant material, being able to degrade the most recalcitrant plant polymers by using their potent enzymes and also via mechanical disruption of lignocellulosic material through their fungal hyphae.