The first comprehensive accounting of Colorado lichen diversity was published in the Catalog of the Colorado Flora: A Biodiversity Baseline (Weber & Wittmann 1992). Subsequent to that publication, two unpublished manuscripts documenting macro- and microlichens were prepared by William Weber as the Catalog of the Lichens of Colorado. In addition to updating the taxonomy and list of taxa of Weber & Wittmann (1992), these annotated checklists included preliminary dichotomous keys to the species. Specimens of some of the taxa included therein were also distributed as Exsiccati from the University of Colorado Museum. Weber (1981) published a list of the first 600 fascicles, with roughly 20% of these consisting of specimens collected in Colorado. One of these (LICH. EXS. COLO No. 24) represented a new species, Psora cerebriformis, from the state. The taxa included in this online version of the Catalog of the Lichens of Colorado, compiled by Scott T. Bates and Ann Henson, are derived from the four source documents described above. The source documents were graciously provided by R.C. Wittmann and W.A. Weber. It is hoped that this checklist will continue to be updated as additional records of Colorado lichens become available.