This article reviews the current state of knowledge about the evolutionary history of lichenized ascomycetes within an integrated system of all ascomycetes. Substantial progress has been made since molecular techniques were applied to unravel evolutionary relationships. Molecular approaches detect how often the lichen symbiosis arose, test current classification concepts, and find the proper placement for species with uncertain relationships. Uncertainties in some evolutionary hypotheses still need to be resolved by studying further genes. The currently available phylogenetic trees show a number of convergent phenotypic developments in lichenized ascomycetes. The current classification of ascomycetes is reviewed in the light of recent molecular data.