This monograph presents the results of research on the morphological and anatomical variability, ecology, and distribution of <em>Opegrapha</em> s. l. in Poland. The study is based on roughly 1,400 specimens from Polish and some European herbaria. Out of the 18 species of the genus <em>Opegrapha</em> s. l. recorded from Poland, seven species belong to the genus <em>Opegrapha</em> Ach., four species now belong to the genus <em>Alyxoria</em> Ach. ex Gray, two species each are found in the genera <em>Arthonia</em> Ach. and <em>Zwackhia</em> Körb, and one species belongs to each of the genera <em>Gyrographa</em> Ertz &amp; Tehler, <em>Phacographa</em> Hafellner, and <em>Pseudoschismatomma</em> Ertz &amp; Tehler. One of the species, <em>Zwackhia sorediifera</em>, has been reported from Poland for the first time. Among the 18 species of the genus <em>Opegrapha</em> s. l., 10 are epiphytic, five epilithic, and two lichenicolous. The first modern identification key for the species of <em>Opegrapha</em> s. l. in Poland is presented. Numerous new regional records are provided that complement our knowledge of the geographic distribution of some poorly known taxa, such as <em>Alyxoria culmigena</em>, <em>A. mougeotii</em>, <em>A. ochrocheila</em>, <em>Arthonia calcarea</em>, <em>Opegrapha dolomitica</em>, <em>O. geographicola</em>, <em>O. lithyrga</em>, and <em>Phacographa glaucomaria</em>. All species are characterized and discussed, and their diagnostic characters illustrated. Geographic ranges of each species in Poland are presented on maps based on revised herbarium materials.