From the rain forests of Costa Rica to the frozen deserts of Antarctica, lichens are a familiar part of the landscape. Widespread and long-lived, yet vulnerable to environmental disturbance, lichens are useful to scientists in assessing the effects of air pollution, ozone depletion, and metal contamination. Illustrated with more than 150 color photographs, reveals the varied and intriguing world of organisms that have been used in natural remedies and are becoming key indicators of the earth's environmental health.