The proportion of older adults (age 65 and older) in oncology practices continues to increase. Older adults present with unique issues that complicate management decisions and evidence from randomized clinical trials to inform management of these patients is lacking. Despite this, principles of geriatric medicine need to be incorporated into oncology practice to provide optimal individualized care to patients. There is increasing evidence from observational studies that geriatric assessment (GA) strategies can be applied in oncology, can help predict treatment outcomes, and can inform supportive care management for older adults. In this review, we discuss the principles of GA and their use in older adults with cancer. In addition, considerations on when to refer to a geriatrician and issues related to management of vulnerable older adults will be addressed.