This publication provides an extensive treatment of the pyrenocarpous lichens with bitunicate asci (excluding Porinaceae, Myeloconidaceae and chiefly saxicolous genera) in Costa Rica, with keys, descriptions, and taxonomic discussion. A total of 181 species is treated, the majority of which are reported from the country for the first time, and several taxa are new to the Neotropics. Names reported or listed by earlier authors, in particular those by Müller Argoviensis and Dodge in the late 19th and early 20th century, were critically revised, and many turned out to belong to other taxa.