Lichens and the tiny animals called tardigrades ("water bears") that live in them are sensitive to certain air pollutants such as sulfur dioxide. Accordingly, they can be useful bioindicators of air quality. Designed to engage students in the scientific process, this Web site, produced by PathFinder Science, offers a learning program based on lichen cover and tardigrade density and diversity on trees. Detailed background information about lichens and tardigrades is provided, as well as explicit instructions for collecting and analyzing data for this study. Results can be submitted to the PathFinder Science network for inclusion in an interactive lichen map of the US. As with other PathFinder Science learning programs, the overall emphasis of this project involves understanding the scientific process, from making initial observations to publishing results. Users should note that the publication submission option is currently down. A relevant doctoral thesis containing a two-week instructional unit (complete with assessment methods) for lichen research has been recently added to the Web site and can be downloaded in Adobe Acrobat (.pdf) format.