A large-scale outbreak of red tide along coastal areas is becoming a global marine hazard, which is associated with fish and shellfish mass mortalities through poisoning. The Seto Inland Sea, the largest semi-enclosed sea in Japan has suffered from red tide outbreaks since the late 1950's. This book discusses the red tide phenomena throughout the world, which includes biological research results on taxonomy of cyst and vegetative cells of red tide organisms and ecological and physiological studies using ecological modeling. This book is undoubtedly useful for scientists and students in the field of biological oceanography, marine environment science and aquaculture, as well as governmental researchers working for the conservation of marine coastal environment.