The document Santesson’s Checklist of Fennoscandian Lichen-Forming and Lichenicolous Fungi provides a comprehensive catalog of lichens and lichen-associated fungi found within the geographical regions of Sweden, Norway, and Finland. It is an updated edition, originally initiated by Rolf Santesson, with substantial revisions and additions since its first publication. The checklist includes over 3,200 species, organized taxonomically and geographically, with distribution data, ecological preferences, and relevant synonymy. The work also highlights species discovered between 2004 and 2021, detailing their growth habitats and associated fungi. This resource is intended to serve as a key reference for botanists and ecologists studying Scandinavian lichens. Fennoscandia, Lichens, Lichenicolous Fungi, Checklist, Biodiversity, Sweden, Norway, Finland, Ecology, Taxonomy