Cortinarius violaceus, commonly known as the violet webcap or violet cort, is a fungus in the webcap genus Cortinarius native across the Northern Hemisphere. The fruit bodies are dark purple mushrooms with caps up to 15 cm (6 in) across, sporting gills underneath. The stalk measures 6 to 12 centimetres (2 1⁄3 to 4 2⁄3 in) by 1 to 2 centimetres (3⁄8 to 3⁄4 in), sometimes with a thicker base. The dark flesh has a smell reminiscent of cedar wood. Forming symbiotic (ectomycorrhizal) relationships with the roots of various plant species, C. violaceus is found predominantly in conifer forests in North America and deciduous forests in Europe.
Though they are sometimes described as edible, the appearance of these mushrooms is more distinctive than their taste. The species was first described by Carl Linnaeus in 1753, and has undergone several name changes. It is the type species of the genus Cortinarius, but is readily distinguished from other species in the genus by its dark colouration and distinct cystidia. There are some populations that seem to prefer deciduous trees and others that prefer pines, but no genetic divergence between the two has been found. When identified as taxonomically separate from the deciduous-preferring populations, the pine-preferring populations have been referred to either as a separate species, C. hercynicus, or as a subspecies, C. violaceus ssp. hercynicus. Other populations once identified as C. violaceus or close to that species have now been described as new and separate species, such as C. palatinus, C. neotropicus, C. altissimus, C. kioloensis and C. hallowellensis.