The book, in its Second Edition, has been thoroughly revised considering the feedback received from the readers. The text has been simplified. New information has been added, and at the same time, extra details have been deleted to make the book concise. The new edition introduces a chapter on Medically Important Snails (Chapter 9). We, the human are the host of many parasites, which cause major public health problems, untold suffering and death. Thus, three major groups of parasites-protozoa (flagellates, amoebas, and malarial parasites), helminthes (flukes, tapeworms, and roundworms), and arthropods (insects and arachnids) have been discussed with suitable illustrations. Morphology, lifecycle, mode of transmission, incidence, symptoms, diagnosis, and prevention of medically important parasites have been discussed in light of recent researches. In addition, the chapters, namely, the Evolutionary Aspects of Hosts and Parasites and Present Trends of Parasitic Importance add further value to the book. The book has been written for the undergraduate and postgraduate students of Zoology and other Life Sciences disciplines. In addition, the medical students, public health workers and health professionals also find this text useful. Key Features: Diagrammatical presentation of life cycle of parasites. Suitably illustrated text. Discusses the food-borne, water-borne and vector-borne parasitic diseases. Contains glossary of important terms.