This chapter investigates the recent results of studies of the ecology of fungal pathogens, including ecological insights obtained by implementation of molecular tools. It spans a spectrum of invertebrates as hosts, although emphasis will be on pathogens of terrestrial insects, which have been the focus of most ecological research. Some taxa of invertebrate pathogenic fungi have evolved adaptations for utilizing living plants as substrates, and these lifestyles have recently received increased attention from researchers following the initial documentations of such plant associations by Beauveria and Metarhizium. This topic has recently been reviewed; the chapter mainly focuses on aspects of ecological relevance, including trophic interactions. Fungal pathogens are used to provide biological control in numerous ways. The primary type of biological control emphasized for fungal pathogens is inundative augmentation, in which biological control agents are applied for immediate impact based on the propagules released.