Diseases and parasites of mollusks were identified as a critical information gap in relation to tropical mollusk aquaculture planning and development. There is bulk of information of research and monitoring on mollusk diseases from temperate waters whereas, little is known about the tropical mollusk diseases. Moreover, the information so far available from the tropics is not reviewed systematically from the diagnosis, prevention and control point of view. Hence, we made an attempt to conduct a review of the existing information on the tropical mollusk diseases. In this book, major parasitic groups affecting mollusks were discussed separately. The scope and structure of this review reflects 6 objectives; these are: 1) to collate and review information on the occurrence of major parasites and diseases of tropical mollusks; 2) to present their geographic distribution; 3) to review the effects of different parasites on their host; 4) to illustrate the life cycles along with the characteristics of the parasites; 5) to accumulate the current diagnostic tools available for the mollusk diseases; and 6) to up-to-date the existing preventive and curative measures against such diseases.