Increased understanding of the mTOR signaling pathway in relation to malignant cells has prompted extensive efforts to develop new therapeutic approaches. The six chapters of this book summarize the current status of efforts using mTOR inhibitors for the treatment of several malignancies. First generation mTOR inhibitors (rapalogues) are now approved by the US FDA for the treatment of renal cancer, and further new drugs may be approved. There is also hope that the second generation of catalytic inhibitors of mTOR that target both TORC1 and TORC2 complexes will be more powerful and effective antineoplastic agents, and clinical trials using such agents are currently ongoing. This book provides a comprehensive review on the emerging roles of mTOR inhibitors in different malignancies in which they have high therapeutic potential.