Since its establishment in the early 1970s, the USDA-ARS Entomopathogenic Fungal Cultures Collection (ARSEF) has grown to become the largest and most comprehensive germplasm repository of fungal strains from insects, other arthropods, and nematodes, particularly those that are agricultural pests or vectors of animal or human disease. The ARSEF actively seeks to acquire and distribute strains to researchers and to provide resources for the isolation, collection, preservation, and identification of fungal strains from invertebrate hosts. The collection serves researchers in basic research in fungal systematics and comparative genomics, fungal genetics, insect pathology, biodiversity studies, as well as applied research and biotechnological development of biological control agents and bioinsecticides for invertebrate pests. The culture collection and its associated collection of microscope slides and herbarium specimens provide invaluable support for taxonomic research on and the diagnosis of fungal pathogens of invertebrates.