The global emergence and spread of the pathogenic fungus *Batrachochytrium dendrobatidis* ( Bd ), which causes chytridiomycosis, has led to the decline or extinction of approximately 200 species of frogs. The authors propose that this fungus is the primary cause of the "enigmatic" declines of frogs, which are not attributed to overexploitation or habitat loss. They present evidence supporting the "novel pathogen hypothesis," which suggests that Bd is a highly pathogenic, virulent, and transmissible fungus that has recently spread to naive frog populations. This hypothesis is supported by the rapid spread of Bd, its high pathogenicity in frogs, and its presence during mass mortality events. In contrast, the "emerging endemic hypothesis" is less parsimonious and lacks strong evidence. The authors emphasize the urgent need for conservation efforts to control and manage chytridiomycosis, including mapping the global distribution of Bd, improving biosecurity, and implementing quarantine and health screening protocols for amphibian trade. They also call for international cooperation between organizations like the Office International des Epizooties (OIE) and the World Conservation Union (IUCN) to develop and coordinate global strategies to abate the threat of chytridiomycosis.The global emergence and spread of the pathogenic fungus *Batrachochytrium dendrobatidis* ( Bd ), which causes chytridiomycosis, has led to the decline or extinction of approximately 200 species of frogs. The authors propose that this fungus is the primary cause of the "enigmatic" declines of frogs, which are not attributed to overexploitation or habitat loss. They present evidence supporting the "novel pathogen hypothesis," which suggests that Bd is a highly pathogenic, virulent, and transmissible fungus that has recently spread to naive frog populations. This hypothesis is supported by the rapid spread of Bd, its high pathogenicity in frogs, and its presence during mass mortality events. In contrast, the "emerging endemic hypothesis" is less parsimonious and lacks strong evidence. The authors emphasize the urgent need for conservation efforts to control and manage chytridiomycosis, including mapping the global distribution of Bd, improving biosecurity, and implementing quarantine and health screening protocols for amphibian trade. They also call for international cooperation between organizations like the Office International des Epizooties (OIE) and the World Conservation Union (IUCN) to develop and coordinate global strategies to abate the threat of chytridiomycosis.