Despite the significant advances in cancer therapy made through constant evaluation and analysis of treatment aftereffects, the disease still remains one of the foremost causes of mortality worldwide killing more than 12 million people annually. The prime reason behind the failure of conventional chemotherapeutics which are used as the chief regimen in the comprehensive treatment of cancers is the development of chemoresistance. It can be either intrinsic or acquired and is primarily mediated via different key regulators like MDR, MAPK, NF-κB, PI3K/Akt, Wnt signaling pathways etc. Thus, agents which can target these regulatory elements or pathways and in turn sensitize cancer cells to chemotherapy holds immense prospect. However, there is barely such comprehensive work available in scientific literature that explains how chemosensitization of cancer cells functions using different drug combinations and exhibit synergism. This book provides a detailed description of chemoresistance and chemosensitization, targets for chemosensitization and various approaches adapted in the process of chemosensitization. Furthermore, the book explicates the role of various chemosensitizers, both natural and synthetic in sensitizing cancer cells and also details the current research findings on chemosensitization of different cancer types in both pre-clinical and clinical settings.