The larval stage of Echinococcus granulosus causes Cystic Echinococcosis (CE), an infection that constitutes a major public health problem in both developing and developed countries. The parasite develops into hydatid cyst, in various organs of different intermediate hosts and humans are accidentally infected. In this book, we present the parasitology and the immunology of CE. The early stages of E. granulosus development and the escape to the host immune system are documented. Protective host immune responses developed during the infection/disease are also discussed in the present work. Moreover, we present the physiological and immunological mechanisms involved in CE, leading to an established infection or in contrast an abortive infection.