This book covers interesting aspects of the tumor microenvironment (TME), its biological functions, regulation, and the challenges it poses to achieving cancer therapy. The TME consists of numerous biological components, including various cell types, cytokines, chemokines, pro-tumor factors, and anti-immune factors, which promote tumor growth, proliferation, tumor survival, anti-apoptosis, and development of tumor drug resistance. This book provides new updates on the biological properties of TME and its impacts on various cancer types.