A key component in healthy ecosystems, lichens can be found in almost any natural habitat in the Pacific Northwest. This comprehensive guide to the region's macrolichens is intended for use by beginners as well as specialists: weekend naturalists will be able to identify specimens and recognize the great diversity of lichens, while lichenologists and mycologists will gain greater knowledge of the distribution and abundance of various species. This updated third edition of Macrolichens of the Pacific Northwest includes 95 additional species and an expanded introduction. It features keys to 109 genera and 681 species of Oregon and Washington macrolichens--all the macrolichens known or expected to occur in the two states. The keys also provide excellent coverage for lichens of Idaho and Montana, inland to the Continental Divide. Color photographs and detailed descriptions emphasize lichens prevalent in forested ecosystems. The illustrated glossary and introductory material cover the terminology needed to identify macrolichens and provide information on collection and handling. The biology, ecology, and air-quality sensitivity of lichens are discussed; regional air-quality sensitivities are provided for nearly 200 species. Macrolichens of the Pacific Northwest will prove invaluable to anyone seeking to identify lichens or to better understand these organisms and their vital role in the natural world.