The phylum Ascomycota is by far the largest group in the fungal kingdom. Ecologically important mutualisticassociations such as mycorrhizae and lichens have evolved in this group, which are regarded as keyinnovations that supported the evolution of land plants. Only a few attempts have been made to date theorigin of Ascomycota lineages by using molecular clock methods, which is primarily due to the lack ofsatisfactory fossil calibration data. For this reason we have evaluated all of the oldest available ascomycetefossils from amber (Albian to Miocene) and chert (Devonian and Maastrichtian). The fossils representfive major ascomycete classes (Coniocybomycetes, Dothideomycetes, Eurotiomycetes, Laboulbeniomycetes,and Lecanoromycetes). We have assembled a multi-gene data set (18SrDNA, 28SrDNA, RPB1 andRPB2) from a total of 145 taxa representing most groups of the Ascomycota and utilized fossil calibrationpoints solely from within the ascomycetes to estimate divergence times of Ascomycota lineages with aBayesian approach. Our results suggest an initial diversification of the Pezizomycotina in the Ordovician,followed by repeated splits of lineages throughout the Phanerozoic, and indicate that this continuousdiversification was unaffected by mass extinctions. We suggest that the ecological diversity within eachlineage ensured that at least some taxa of each group were able to survive global crises and rapidlyrecovered.