Phacopsis is a genus of lichenicolous fungi distributed worldwide on members of the Parmeliaceae s. ampl. The genus is characterized using current concepts, and its delimitation and family position are discussed. Thirteen taxa are accepted and a key supplied together with new data on their host specificity and distribution. In this genus ascospore shape as well as color and amyloidity of the hypothecial hyphae proved to be major diagnostic characters. Phacopsis falcispora Triebel & Rambold, P. falcispora var. sipmanii Diederich & Triebel, P. lethariellae Hafellner & Rambold, P. menegazziae Triebel & Rambold, P. oxyspora var. defecta Triebel & Rambold, and P. oxyspora var. fusca Triebel & Rambold are described as new. Phacopsis oxyspora (Tul.) Triebel & Rambold and P. vulpina Tul. are lectotypified. Emended descriptions of P. oxyspora var. oxyspora, P. pro- lificans (Muill. Arg.) Triebel & Rambold, and P. rufa (Miill. Arg.) Triebel & Rambold and notes on other species of the genus are given. Phacopsis is a genus of obligately lichenicolous fungi which is distributed worldwide on foliose and fruticose taxa of the lichen family Parmeliaceae. Species of Phacopsis are easily recognized by their growth habit, in particular the subimmersed, shiny brown to black apothecia which are often found aggregated on galls of the host lichens. The genus is currently placed in the family Lecanoraceae (Haf- ellner 1987), which means that its closest relatives are presumably lichens. Because of an increasing interest in these commonly collected lichenicolous fungi, a conspectus of the genus seems timely.