Although the incidence of cancer in the United States is high, improvements in early diagnosis and treatment have significantly increased survival rates in recent years. Many survivors of cancer experience lasting, adverse effects caused by either their disease or its treatment. Physical therapy interventions, both established and new, often can reverse or ameliorate the impairments (body function and structure) found in these patients, improving their ability to carry out daily tasks and actions (activity) and to participate in life situations (participation). Measuring the efficacy of physical therapy interventions in each of these dimensions is challenging but essential for developing and delivering optimal care for these patients. This article describes the acute and long-term effects of cancer and its treatment and the use of the World Health Organization's International Classification of Functioning, Disability and Health (ICF) as a basis for selection of assessment or outcome tools and diagnostic or screening tools in this population.