Pathogenic fungi represent a persistent and severe threat to overall agricultural productivity, ecosystem stability, and human health through diverse infection mechanisms. This chapter describes an organized, structured, mechanism-based perspective of the interaction between fungal–host cells with respect to the progression of successful infection. It highlights the initial progression of disease from host surface perception, adhesion, and mechanosensing mediated by fungal adhesins, mechanosensors, and downstream signaling pathways. These early events drive the differentiation of infection structures such as appressoria, which generate high turgor pressure through osmoprotectant accumulation and melanin deposition to facilitate host entry. After this entry, a continuation of the formation of intimate host–pathogen interfaces is described, including the production of extra-invasive hyphal membranes and effector-secretion sites. Emphasis is placed on the trafficking of secreted fungal effectors into host cells, as well as their roles in suppressing immunity, metabolism modulation, and regulation of vesicle trafficking and cytoskeleton activities. Host defense responses are discussed within the framework of an integrated immune continuum, in which pattern-triggered immunities operate through shared signaling molecules, including reactive oxygen species, calcium fluxes, and kinase cascades. Infection outcomes are further assessed in terms of host cell death programs, nutrient acquisition strategies, and host susceptibility. This chapter also highlights the genomic adaptability of fungal pathogens, focusing on rapidly evolving effector genomes and mobile elements. Finally, this chapter addresses the experimental hurdles in tackling fungal pathogenesis through the use of genome editing and RNA interference techniques to combat fungal diseases. Collectively, this chapter provides an integrated cellular and molecular perspective on fungal pathogen biology.