It is now 17 years since the junior author's book Parasitic protozoa was first published, and 13 years since it received limited revision. The study of symbiotic protozoa has meanwhile progressed, and much of the content of the earlier book has been superseded if not displaced by recent knowledge. We believe that there is still a place for an introductory textbook, conventionally arranged on a taxonomic frame work, on this most fascinating group of organisms. It should supplement (certainly not supplant) more modern treatments from different angles. A mountain looks very different if one...