Trichoderma is one of the most studied genera of ascomycetous fungi due to the beneficial effects it has on plants. Trichoderma spp. are involved in the production of cell wall-degrading enzymes and metabolites with antimicrobial activity. It also produces volatile compounds that act together as direct biocontrol agents to protect plants against phytopathogenic fungi, oomycetes, nematodes and bacteria. Trichoderma spp. can also compete in the rhizosphere for space and nutrients while it can also protect plants by activating systemic immune responses that result in a faster and stronger induction of plant basal resistance mechanisms against biotic and abiotic stresses. The possibility that Trichoderma can also promote plant growth opens new opportunities to register strains as biostimulants. Adequate registration procedures are urgently needed as there is no appropriate legal framework for registering Trichoderma as both plant protection products and as biofertilizers.