The incidence and prevalence of most cancers increase with age. The reasons for this may include tumor escape mechanisms and decreased immunosurveillance, but most are caused by the time required for carcinogenesis, according to most scientists. The immune system is a unique mechanism of defense against pathogens and possibly cancers; however, there is a body of evidence that the immune system of the aged is eroded, a phenomenon termed immunosenescence. There is a growing interest in immunosenescence and how it may contribute to the increased number of cancers with aging. Each arm of the immune system, innate and adaptive, is altered with aging, contributing to increased tumorigenesis. Understanding the contribution of immunosenescence to cancer development and progression may lead to better interventions for the elderly.