The fact that this textbook has gone into a fourth edition is evidence of its value. It has been eight years since the third edition appeared, and, although there have been no changes in the table of contents, the book has been enlarged, the number of illustrations has been increased, and many improved drawings have replaced older ones. Many new references have been added. The author index is now separate from the subject index, and the author has achieved his goal to set forth "introductory information on the common and representative genera of all groups of both free-living and parasitic Protozoa." The new edition should be a welcome addition to the library of public health workers, students of biology, laboratory workers engaged in identification of unknown specimens, and all persons whose work involves familiarity with protozoa.