The paper documents 70 species of fungi found on species of the lichen genus Cladonia, 65 of which are obligately lichenicolous. One genus, Brackelia, and seven species, Biciliopsis cladoniae, Brackelia lunkei, Caeruleoconidia biazrovii, Neolamya ahtii, Niesslia keissleri, Sclerococcum crassitunicatum and S. epicladonia, are here described as new to science. The names Caeruleoconidia and C. ochrolechiae are validated. Ameroconium cladoniae is considered as a heterotypic synonym of Taeniolella beschiana. Merismatium cladoniicola most likely is a heterotypic synonym of M. decolorans. Taxonomic notes on critical specimens, including those of Abrothallus cf. pezizicola, Arthonia cf. lepidophila, Cladophialophora cf. cladoniae, Hainesia cf. bryonorae, Merismatium cf. nigritellum as well as of unidentified species of Acremonium, Dactylospora, Leptosphaeria, Lichenopeltella and Pronectria found on Cladonia are provided. Cercidospora cladoniicola, Didymocyrtis cladoniicola, Hainesia longicladoniae, Pezizella ucrainica, Plectocarpon cladoniae and Polycoccum laursenii are documented as new to Asia. Biazrovia stereocaulicola, Hainesia longicladoniae and Polycoccum microcarpum are new to North America. The following species are new to various countries: Argentina (Bachmanniomyces uncialicola and Niesslia cladoniicola), Finland (Didymocyrtis foliaceiphila and Roselliniella cladoniae), Japan (Lichenosticta alcicorniaria), Lithuania (Abrothallus cf. pezizicola), Mongolia (Arthonia digitatae, Didymocyrtis cladoniicola, Epicladonia stenospora s. lat., Lichenostigma alpinum s. lat., Phaeopyxis punctum, Sphaerellothecium cladoniicola and Taeniolella beschiana), New Zealand (Abrothallus cladoniae s. lat. and Epicladonia sandstedei), Norway (Arthonia digitatae), Kazakhstan (Sphaerellothecium cladoniae), Kyrgyzstan (Epicladonia sandstedei), Papua New Guinea (Opegrapha cladoniicola), Portugal (Epicladonia stenospora s. lat.), Russia (Abrothallus cladoniae s. lat., A. cf. pezizicola, Arthrorhaphis aeruginosa, Didymocyrtis foliaceiphila, Hainesia longicladoniae, Neoburgoa freyi, Pezizella ucrainica and Polycoccum laursenii), Spain (Lichenoconium aeruginosum), U.S.A. (Biazrovia stereocaulicola, Hainesia longicladoniae, Niesslia cladoniicola and Polycoccum microcarpum), Venezuela (Roselliniella cladoniae) and Vietnam (Pyrenidium actinellum s. lat.). Epicladonia sandstedei and E. stenospora s. lat. are new to Macaronesia. Heterocephalacria bachmannii is for the first time documented in the polar desert biome. Biazrovia stereocaulicola, Coniochaeta sp., Merismatium coccisporum and Pyrenidium actinellum s. lat. are newly reported to occur on Cladonia. A key to 138 species of fungi so far known to occur on Cladonia is provided. Cladoniicolous fungi, new taxa, new records, new host lichens, taxonomy