After devastating vast ranges of pine forests in Asian countries, Pine Wilt disease invaded European forests, becoming a worldwide threat. Originating in North America, the pathogen of this forest epidemic is a nematode, a long filamentous organism, only 1mm in length. Nematodes are carried from tree to tree by a long-horned beetle, where they lurk in its trachea and thereby spread the disease. The challenges raised for researchers to develop effective control methods were to discover how such tiny nematodes infect and kill large pine trees within a short period, and how the infection spreads repeatedly each year. Other key issues include how giant pine trees die within a short period of time due to infection by these small nematodes, how various organisms involved in this disease correlate to each other, how host trees differently respond to nematode invasion among pine species, and how environmental factors affect the progression and spread of the disease. This book is a record of the fantastic and ingenious research by many tenacious researchers who have worked to clarify these issues. Information on a wide range of fields, from molecular biology to microbiology, nematology, entomology, botany, and ecology, has been incorporated into pine wilt research. Therefore, this book will greatly stimulate the curiosity and research motivation of those interested in field biology and the conservation of the natural environment.