Protozoa is an important component in food webs in the aquatic ecosystem, and exhibits many of the characteristics of structure and function of entire aquatic ecosystems. PFU protozoan communities play the substantial role and show the clear advantage in bio-monitoring with relation to water quality. This paper makes a systematic exposition on the aspects of ecological basis and application of PFU protozoan community. The case studies of the different types of water quality in China and other countries, car...