An annotated checklist of the lichens of Hong Kong, based on all available literature reports and specimens, including those recently collected by the authors, is presented. In total, 261 species are reported, of which 176 are new records for Hong Kong, 132 of which are new for China, 43 are new for East Asia, and 27 are new for Asia. The lichen vegetation is mainly tropical, as is shown by the distribution patterns of the identified species: 53 species are cosmopolitan, 40 northern temperate, 122 pantropical, 17 paleotropical and 29 endemic to tropical East Asia. With regard to substrata, 129 species are corticolous, 148 saxicolous, 17 foliicolous and 19 terricolous. Four species are newly described: Anisomeridium conorostratum Aptroot, A. hydei Aptroot, Caloplaca pulicarioides Aptroot and Placidiopsis poronioides Aptroot. The flora is rather poor in species; for example, no Caliciales have been found. In the past, the numbers of species of several groups such as the Graphidaceae, Heterodermia and Xanthoparmelia have been overestimated, whereas few pyrenocarps have been reported. The flora of wet granitic outcrops is surprisingly well developed in Hong Kong. Although not a single Peltula species was reported before, six species were identified, including one that was previously only known from Africa. In addition, several other cyanophilic genera are present, such as Euopsis, Psorotichia, Pyrenopsis and, most unexpectedly, Vestergrenopsis, each with one species. A comparison between old and recent records shows that many Lobarion species are now extinct. The drastic decline of species of the Lobarion vegetation indicates that air pollution and other habitat disturbances, mainly deforestation, to which these species are very sensitive, are seriously threatening the lichen biodiversity of Hong Kong.