Identification of protozoan parasites in animal tissues is often difficult and confusing. The purpose of this atlas is to create a single reference containing illustrations of the numerous species of protozoans and their stages as they appear within infected tissues. This atlas provides 257 color photographs of these organisms, as well as 36 color photomicrographs of fungi, prepared by techniques that best identify them. It also includes simplified life-cycle drawings as well as brief descriptions of the parasites, hosts, transmission, and pathogenesis. This second edition includes minor textual changes and profound enhancement of the color photographs. The illustrations in this atlas represent the most common stages under optimal conditions for identification. This atlas is intended as an aid for students, teachers, diagnosticians and researchers by facilitating identification of protozoan parasites of animals.