The risk of cancer increases with age, and as the US population rapidly ages, the number of older adults seeking treatment for cancer is also increasing dramatically. However, this growing population of older adults has been underrepresented in clinical trials that set the standards for oncology care. In addition, most clinical trials conducted to date have not addressed the problems that accompany aging, including reduced physiologic reserve, changes in drug pharmacokinetics, and the impact of comorbid medical conditions and polypharmacy on treatment tolerance. As a result, there are variations in treatment patterns between older and younger adults and few evidence-based guidelines accounting for the changes in physiology or pharmacokinetics that occur with aging. This article examines the demographics of cancer and aging, the barriers to enrollment of older adults on clinical trials, and approaches for future trials to address the needs of the older patient.