Frailty is one of the most important determinants of health and health outcomes, and is increasingly recognised as a growing health burden as the older population increases across the world. Frailty is of particular interest in older people with cancer where it is associated with increased risk of postoperative complications, chemotherapy intolerance, disease progression, hospitalisation and death, as well as poor quality of life, functional and cognitive decline, depression and institutionalisation. Early research in geriatric oncology focused on the heterogeneity in the health status of the older population, highlighting the limitations of performance status used in standard oncologic workup to capture this adequately. Subsequent works looked at the concept of frailty and multidimensional evaluation by geriatric assessment. The current evidence supports screening and assessment for frailty to guide treatment planning and optimise care for patients with cancer. The gold standard for frailty assessment is the comprehensive geriatric assessment, a multidimensional, multidisciplinary process to identify medical, social and functional needs and manage elderly patients. However, because of the challenges with time and resourcing to complete a comprehensive geriatric assessment in oncology practice, some have advocated for a two-step approach using brief frailty measures to screen for patients who might benefit from a comprehensive geriatric assessment or, alternately, a modified geriatric assessment approach. Frailty screening and assessment should consider a person’s health conditions and medications, physical performance, nutritional status, cognition, mental health and social supports, as well as resiliency factors that protect against adverse health outcomes and promote wellbeing. The results should be incorporated into the oncologic decision-making and individualised management strategies to optimise care for patients with cancer, underpinned by a shared decision-making approach to address what matters to the patient.