The order Onygenales includes several important ketatinophilic fungal organisms that cause or are associated with dermatologic disease in reptiles. Ophidiomyces ophidiicola is the causative agent of ophidiomycosis, or “snake fungal disease”, which has been reported in over 60 snake species across multiple continents in both wild populations and managed care settings. Fungi in the genus Nannizziopsis infect lizards, crocodilians, snakes, chelonians, and humans and cause “yellow fungus disease” in bearded dragons (Pogona spp.). Nannizziopsis spp. are associated with dermatomycosis in multiple reptile species in the pet trade and in wild populations in Australia. Emydomyces testavorans is associated with severe skin and shell disease in over 60 chelonian species, and is currently a pathogen of significant management and conservation concern for threatened North American aquatic turtles. Paranannizziopsis spp. have been isolated from cases of dermatomycosis in lizards, tuatara, and snakes, including invasive species which could introduce this pathogen into sensitive, naïve reptile communities. These fungi are the subject of significant research effort and our understanding of their epidemiology and clinical management is constantly expanding. This master class will review currently available knowledge about infections with Ophidiomyces ophidiicola, Nannizziopsis spp., Emydomyces testavorans, and Paranannizziopsis spp., including conservation significance, epidemiology, affected species, clinical presentation, diagnostic methods and evidence-based sampling strategies, biosecurity and disinfection protocols, and treatment recommendations. This will provide a strong foundational knowledge base about these emerging fungal pathogens for reptile clinicians.