Background: Structured care processes that provide a framework for how oncologists can incorporate geriatric assessment (GA) into clinical practice could improve outcomes for vulnerable older adults with cancer, a growing population at high risk of toxicity from cancer treatment. We sought to obtain consensus from an expert panel on the use of GA in clinical practice and to develop algorithms of GA-guided care processes. Methods: The Delphi technique, a well-recognized structured and reiterative process to reach consensus, was used. Participants were geriatric oncology experts who attended NIH-funded U13 or Cancer and Aging Research Group conferences. Consensus was defined as an interquartile range of 2 or more units, or 66.7% or greater, selecting a utility/helpfulness rating of 7 or greater on a 10-point Likert scale. For nominal data, consensus was defined as agreement among 66.7% or more of the group. Results: From 33 invited, 30 participants completed all 3 rounds. Most experts (75%) used GA in clinical care, and the remainder were involved in geriatric oncology research. The panel met consensus that “all patients aged 75 years or older and those who are younger with age-related health concerns” should undergo GA and that all domains (function, physical performance, comorbidity/polypharmacy, cognition, nutrition, psychological status, and social support) should be included. Consensus was met for how GA could guide nononcologic interventions and cancer treatment decisions. Algorithms for GA-guided care processes were developed. Conclusions: This Delphi investigation of geriatric oncology experts demonstrated that GA should be performed for older patients with cancer to guide care processes.