Book excerpt: Ciliated protozoa are one of the most relevant biological communities in the reactors of wastewater treatment plants. These organisms are excellent tools to assess the biological status of the reactor being used to monitor wastewater treatment plants performance. This book has been designed to simplify identification of ciliates, bearing in mind the difficulties on the manipulation and proper identification of these species. The specific role of ciliates in WWTP is discussed; methods for observation together with a glossary of scientific words and a simple and easy key to the taxonomic groups of ciliates are also provided. Illustrations, drawings, photographs and brief morphological descriptions of the species are included. Guidelines for the Identification of Ciliates in Wastewater Treatment Plants is the first book to use the new official classification proposed by the Society of Protozoologists (2005). It includes a complete chapter on methodology that is designed to be easy to follow and reproduce. A simple key to classify main taxonomic groups and genera is included, as are detailed descriptions to aid observation and identification of species of ciliates, in addition to drawings and photographs that accurately reproduce ciliate species.