Starting with a look at how lichens have been used throughout history in medicines, dyes, food and perfumes, this study then goes on to describe what lichens are, and how they grow and reproduce. A detailed survey is given of the range of habitats in which lichens can be found: on trees, rocks, heaths and moors, chalk and limestone, mountains, rivers, lakes, the coast, walls and buildings, most famously on churches and in churchyards. Gilbert also discusses the susceptibility of lichens to air pollution, and how they can be used to detect environmental pollution.