In the author's statement, this book represents an expanded version of lectures … to postgraduate students … and medical officers … taking short courses in tropical diseases and parasitology. It covers the parasitic protozoa with attention directed mainly to those of medical importance. The style is easy reading for the student and the content is accepted facts with pertinent theories and occasional mention of frontiers of investigation in well organized fashion. Part I presents the morphology, reproduction, physiology, nomenclature, classification and ecology (host-parasite relations, drug action and geographic distribution) of protozoa in an elementary but comprehensive manner. Here the terms “definitive” and “intermediate” hosts are properly considered inappropriate for protozoa but the reader may also object to the term “final” host as used for the vertebrate host. The term “zoonose” for a disease common to man and lower mammals is probably appreciated more by the author than the reader.