General properties of all cancers include uncontrolled cell growth and, in most instances, the ability to metastasize, or spread to other areas of the body. The chapter deals with cytokines that have been extensively investigated in the search for both a cause and cure for cancer. Depending upon the type of tumor, roles have been discovered for numerous cytokines in both the genesis and the treatment of cancer. Cytokines produced by tumor cells or tumor stroma can stimulate the survival, proliferation, and metastasis of cancer cells. While numerous cytokines have been evaluated in clinical trials, the greatest potential for cytokine therapy appears to be in combination with other biologic therapies, including monoclonal antibodies, cellular therapies, and cancer vaccines. A careful consideration of the factors responsible for the development, and progression of cancers, and the cytokine milieu of the tumor environment is critical when considering cytokine or anticytokine therapy for this disease. The inflammatory process and in particular, proinflammatory cytokines have been implicated in the process of carcinogenesis and tumor progression.