This book focuses on the emerging research in the field of treatment of solid tumors or cancer with new drug delivery systems using nanotechnology. Nanotechnology has given us a good scope for development of new innovative drug delivery strategies to increase the therapeutic efficacy of anticancer drugs with reduced off-target side effects. Cancer is one of the main causes of death worldwide due to the limitations of classical therapies such as low solubility of active drugs, toxic side effects on healthy cells and resistance of tumor cells. These issues are partly solved by the recent development of polymeric nanoparticles, which improve drug absorption and the therapeutic index, while reducing side effects. Drug carriers must be biocompatible, biodegradable and non-immunogenic. Coupled to a ligand that has affinity for that particular cell, polymeric nanoparticles are used to target specifically malignant cells or tissues and, in turn, improve drug stability. This book presents the latest advances in the application of polymeric particles for cancer treatment, with focus on the tumor microenvironment, synthesis, active and passive targeting, patents, targeting over-expressed receptors, tumor-targeting ligands, theranostics, glioblastoma tumors, lung cancer, breast cancer, prostate cancer and pH-responsive nanoparticles