Trichoderma is a genus of common filamentous fungi with a wide range of lifestyles and interactions with plants, animals, and other fungi. Some Trichoderma strains are used for biological control of plant diseases due to their ability to stimulate plant growth and defense. This review discusses recent advances in molecular ecology and genomics, indicating that saprotrophy on fungal biomass (mycotrophy) and various forms of parasitism on other fungi (mycoparasitism), combined with broad environmental opportunism, have driven the evolution of Trichoderma interactions with plants and animals. Trichoderma species are among the most commonly isolated saprotrophic fungi, found in soil and on various substrates. They exhibit pleiomorphism, existing in two morphologically and physiologically different stages. The sexual (teleomorphic) stage is known as Hypocrea, while the asexual (anamorphic) stage is Trichoderma. Many species have lost their ability to reproduce sexually and are now clonal or agamospecies. However, the majority of genetic diversity is represented by sexual forms. Mycoparasitic species of Hypocrea/Trichoderma can degrade and grow within the resting structures of plant pathogenic fungi. Recent genome sequencing of H. atroviridis and H. virens, along with associated "omics" technologies, has provided new insights into the ecology and evolution of Trichoderma. These studies emphasize that mycotrophy, including mycoparasitism, is a widespread property among Trichoderma species and is key to understanding their interactions with other organisms. Trichoderma species interact with other fungi through necrotrophic hyperparasitism or mycoparasitism. These interactions involve proteases and oligopeptide transporters, which are expressed before and at contact with the prey. The actions of these proteases may release oligopeptides that bind to receptors sensing nitrogen starvation. Class IV G-protein coupled receptors (GPCRs) in H. atroviridis may act as sensors for these oligopeptides. Trichoderma species can also colonize plant roots and induce plant defense responses. They may use lectins and proteins with carbohydrate binding domains to attach to the prey. The presence of potential fungal preys and plant root-derived nutrients in the rhizosphere may have been major attractors for the evolution of Trichoderma ancestors towards colonizing the rhizosphere. Trichoderma species can promote plant growth by enhancing root elongation and biomass. They may also induce systemic resistance in plants, leading to the synthesis of defense-related compounds. Trichoderma species can act as endophytes, growing inside plant tissues without causing symptoms. Some species can colonize immunocompromised humans, highlighting their potential as pathogens. The genomes of Trichoderma species contain genes for various enzymes and secondary metabolites, which may contribute to their ability to antagonizeTrichoderma is a genus of common filamentous fungi with a wide range of lifestyles and interactions with plants, animals, and other fungi. Some Trichoderma strains are used for biological control of plant diseases due to their ability to stimulate plant growth and defense. This review discusses recent advances in molecular ecology and genomics, indicating that saprotrophy on fungal biomass (mycotrophy) and various forms of parasitism on other fungi (mycoparasitism), combined with broad environmental opportunism, have driven the evolution of Trichoderma interactions with plants and animals. Trichoderma species are among the most commonly isolated saprotrophic fungi, found in soil and on various substrates. They exhibit pleiomorphism, existing in two morphologically and physiologically different stages. The sexual (teleomorphic) stage is known as Hypocrea, while the asexual (anamorphic) stage is Trichoderma. Many species have lost their ability to reproduce sexually and are now clonal or agamospecies. However, the majority of genetic diversity is represented by sexual forms. Mycoparasitic species of Hypocrea/Trichoderma can degrade and grow within the resting structures of plant pathogenic fungi. Recent genome sequencing of H. atroviridis and H. virens, along with associated "omics" technologies, has provided new insights into the ecology and evolution of Trichoderma. These studies emphasize that mycotrophy, including mycoparasitism, is a widespread property among Trichoderma species and is key to understanding their interactions with other organisms. Trichoderma species interact with other fungi through necrotrophic hyperparasitism or mycoparasitism. These interactions involve proteases and oligopeptide transporters, which are expressed before and at contact with the prey. The actions of these proteases may release oligopeptides that bind to receptors sensing nitrogen starvation. Class IV G-protein coupled receptors (GPCRs) in H. atroviridis may act as sensors for these oligopeptides. Trichoderma species can also colonize plant roots and induce plant defense responses. They may use lectins and proteins with carbohydrate binding domains to attach to the prey. The presence of potential fungal preys and plant root-derived nutrients in the rhizosphere may have been major attractors for the evolution of Trichoderma ancestors towards colonizing the rhizosphere. Trichoderma species can promote plant growth by enhancing root elongation and biomass. They may also induce systemic resistance in plants, leading to the synthesis of defense-related compounds. Trichoderma species can act as endophytes, growing inside plant tissues without causing symptoms. Some species can colonize immunocompromised humans, highlighting their potential as pathogens. The genomes of Trichoderma species contain genes for various enzymes and secondary metabolites, which may contribute to their ability to antagonize