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. Protozoa can thus be used to illustrate biological principles. 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. The guide has been welcomed by professional practitioners, researchers and instructors, by graduate, undergraduate and secondary level students, in a wide range of disciplines, for its clarity in providing a logical system for learning and recognition, the first step towards understanding and using the protozoan community as a biological indicator of environmental change, pollution and contamination.