Witches' broom is an important Southern and Central American disease of cocoa that is estimated to reduce annual world production by some six to seven percent. The disease is still spreading into currently unaffected cocoa-producing areas. This book describes the results of an authoritative, international study resulting from the collaboration among plant pathologists in South America and the Caribbean with centres of expertise in the USA and UK. A series of comparative experiments were established under different climate and disease pressure conditions in six countries. This book describes the experimental methods, comparative analyses and the conclusions drawn from these experiments.