This book is one of the series of "International Top-level Forum on Engineering Science and Technology Development Strategy", arounding the theme of "From virus to tumor, from etiology to protection". This forum was held by Chinese Academy of Engineering, organized by China Medical University etc. in April 2013. Malignant tumors are among the most important risks for human health. In this book, the glorious achievements in elucidating molecular mechanisms of virus and tumor genesis in the past few decades were reviewed; more importantly, it focused on how to transform the brilliant discoveries into clinical practices. The forum provides Chinese scientists an unparalleled plantform for latest information on viral infection and tumorigenesis, clinical prevention and management, and will definitely promote the cooperation between Chinese scientists and their foreign counterparts in the future.