Hybrids are chimeric organisms that result from the crossing of two genetically divergent lineages. Compared to their parents, hybrids sometimes show higher adaptive capacities towards specific niches, thereby contributing to diversification (Abbott et al., 2013). Fungal hybrids have been neglected by formal studies for a long time due to the inherent challenges of the microbial species concept and the difficulty of identifying hybrids based on morphological characters (Gabaldoń, 2020a;Boekhout et al., 2021). Although the first fungal hybrids were identified in Saccharomyces, thanks to careful dissection of metabolic properties (Morales and Dujon, 2012) and emerging genome sequencing technologies (Hittinger, 2013), it was the spread of these sequencing technologies that revealed the true pervasiveness of hybrids across the fungal tree of life (Naranjo-Ortiz and Gabaldoń, 2020; Gabaldoń, 2020b). Sequencing techniques, particularly genomic approaches, have not only unearthed the hybrid nature of many fungal organisms, but also serve as ideal tools for the study of hybrids. Hybrids have chimeric genomes, which usually display high instability and are subject to evolutionary pressures that are different from that of non-hybrid genomes (Runemark et al., 2019). Understanding how hybrids are formed, how they cope with their chimeric genomes, and how they evolve and adapt to distinct environments is a matter of intensive research. This Research Topic gathers six outstanding contributions that use genomic approaches to tackle diverse questions that relate to fungal hybrids.One article by Ament-Vela ́squez et al. provides a compelling example of how genomics can reveal past hybridization, in this case in the lichen-forming Letharia. Guided by unexpected findings of triploid-like individuals, they used genomics to determine that these are hybrids between L. lupina and a so-far-undescribed Letharia lineage. Three other articles focus on the aftermath of hybridization at different time scales in the genus Saccharomyces. The article by Drouin et al. tests the genomic shock Frontiers in Fungal Biology frontiersin.org 01