Hypoxia is a typical microenvironmental characteristic of many solid tumors. HIF-1 is the key regulator of growing tumor's response to hypoxia. HIF-1 subunit levels rise in hypoxic environments, when oncogenes are activated, and/or when tumor suppressor genes are inactivated, this is necessary for HIF-1 function in tumors. HIF-1 turns on genes that enable cells of a solid tumor to flourish in the noxious hypoxic tumor environment via attainment of numerous cancer hallmarks. This book elaborates the regulation and role of HIF-1 in oncogenic signalling. Further, its potential as a drug target for solid tumors is also discussed. The book will be useful as a reference book for students of graduate and post-graduate level courses in Life Science, Biomedical Science as well as to those who have a special interest in Cancer Biology.