Lichens, small and unobtrusive organisms, are seldom noticed as they cling to rocks, trees, and soil in fragile veils or crusts of splendid color and ornate textures. Their beauty is captivating and fascinating, and their purpose and origins are thought-provoking. Lichens make particularly good "bioindicators". They are bioindicators of sulfur dioxide (S0[subscript 2]), fluoride, and ammonia. As with many bioindicators, lichen damage patterns alone cannot establish a totally causal link to atmospheric quality, but they can lead students in a systemic approach to studying the world without great financial cost, while simultaneously investigating general processes of science, atmospheric quality, and lichen biology. This article describes a unit of lichen study. The lichen study encourages students to conduct investigations, use various higher-level thinking skills, improve active participation in group work, and apply conclusions to work towards improvements in their community. Ultimately, using lichens as bioindicators is a powerful classroom activity that employs a cost-effective means for measuring local air quality, while simultaneously teaching aspects of plant biology, air chemistry, weather, and science process. (Contains 1 figure and 1 resource.)