Mainland Portugal has a lichenological tradition spanning more than three centuries, yet it still lacks a modern, critically revised checklist of its lichen biota. This gap is particularly relevant given the increasing role of species checklists as authoritative references for DNA metabarcoding applications and the expansion of large biodiversity datasets, including those derived from citizen science initiatives. Here we present the first comprehensive checklist of lichens and lichenicolous fungi recorded from Mainland Portugal, based on the critical assessment of 43,718 bibliographic records drawn from 381 publications issued between 1788 and 2021. A total of 2012 species and infraspecific taxa are documented from a universe of 4440 taxonomic names, including synonyms. Nomenclature was updated in accordance with the ITALIC 8.0 database. Species distributions are provided by province, following the scheme adopted in Portuguese botanical floras, with additional information on substrates and altitudinal ranges where available. With over 2000 taxa recorded, Mainland Portugal can be considered a lichen-rich territory relative to its land area, comparing favourably with other European checklists. We discuss the factors underlying this diversity, with particular emphasis on the biogeographical position of Portugal at the south-western edge of the European continent. Keywords: biodiversity; Iberian Peninsula; lichenised fungi; nomenclature; taxonomy; Western Europe.