Trichoderma (teleomorph Hypocrea) is a fungal genus found in many ecosystems. Trichoderma
spp. can reduce the severity of plant diseases by inhibiting plant pathogens in the soil through
their highly potent antagonistic and mycoparasitic activity. Moreover, as revealed by research in
recent decades, some Trichoderma strains can interact directly with roots, increasing plant
growth potential, resistance to disease and tolerance to abiotic stresses. This mini-review
summarizes the main findings concerning the Trichoderma–plant interaction, the molecular
dialogue between the two organisms, and the dramatic changes induced by the beneficial fungus
in the plant. Efforts to enhance plant resistance and tolerance to a broad range of stresses by
expressing Trichoderma genes in the plant genome are also addressed.