Book excerpt: Protozoa may be found in almost every aquatic habitat, each containing dozens of species. The diversity can provide invaluable insights into the nature of the habitat and can be used as an indicator of environmental change, pollution and contamination. This colour guide makes the identification of individual protozoa easily accessible to students and professionals and provides information on protozoan communities found in different environments by means of a wealth of colour photomicrographs supported by original and detailed line drawings and concise text.