Abstract: Plant endophytes are microorganisms that colonize plant tissues without causing disease and are widely involved in helping plants cope with various biotic stresses. This review evaluates the capacity of endophytes to resist biotic threats, including pathogenic fungi, pathogenic bacteria, viruses, pathogenic nematodes, and insect pests. It summarizes the mechanisms by which endophytes enhance plant resistance to biotic stresses from four perspectives: competition for resources and ecological niches, secretion of bioactive metabolites, induction of plant resistance, and regulation of plant metabolism and volatile emissions. Furthermore, it reviews the applications of plant endophytes as biopesticides, biofertilizers, and their roles in ecological restoration. The existing challenges, key scientific issues and future research trends are highlighted.