Introduction: Colorectal cancer (CRC) survivors may experience functional deficits due to cancer-associated impairments. However, we do not understand their type and extent of functional deficits and how we could measure the associated cause of functional deficits, such as fatigue. As the survival of CRC survivors improves, the burden of living with functional deficits can be high. Purpose: My research program aims to understand (1) the functional changes and deficits that CRC survivors experience and (2) how to best measure fatigue in this population. Methods: To address the first aim, we used the data from the International Study of the Risk Factors for Gastrointestinal Bleeding and Cardiovascular Events after Gastrointestinal Bleeding to examine individuals’ functional abilities within 1 year of gastrointestinal cancer diagnosis (CRC being the most prevalent type). For the second aim, we conducted a systematic review on fatigue measures in adults with inflammatory bowel disease (IBD) because the causes, severity, and impact of IBD and CRC- related fatigue might be similar. We identified fatigue measures in the IBD population, appraised their psychometric properties, and recommended the most psychometrically robust and feasible measures for clinical and research use, indicating the optimal measures for CRC survivors. Results: After gastrointestinal cancer diagnosis, the majority (~70%) performed fewer functional tasks, mostly in the instrumental activities of daily living; and about 44% had more difficulty walking. Our review identified 16 measures, reviewed the content and psychometric properties, and recommended the Functional Assessment of Cancer Therapy Instrument-Fatigue and the IBD- Fatigue scale for research and clinical use in IBD and CRC populations. Conclusion: We provided a novel understanding of the functional deficits that CRC survivors experience and recommended the optimal measures for assessing CRC-related fatigue. As CRC survivors commonly experience fatigue, fatigue should be measured to understand its role in the functional abilities of CRC survivors. / Thesis / Master of Science Rehabilitation Science (MSc) / More people are living with colorectal cancer (CRC), but may have problems performing their daily activities (i.e. functional problems) due to cancer-associated impairments. However, we do not understand the extent of these impairments and functional problems. We used a sample of people with newly-diagnosed gastrointestinal cancer (CRC being the most common type) to understand their type and extent of functional problems. People were found to participate less in functional activities and particularly have more difficulty walking after a cancer diagnosis. Fatigue is common among those with CRC and may primarily cause functional problems. However, it is not commonly measured, and it is unclear how to best measure fatigue among them. Therefore, we reviewed key qualities of 16 fatigue measures in a similar population (inflammatory bowel disease, IBD) and recommended the Functional Assessment of Cancer Therapy Instrument-Fatigue and the IBD-Fatigue scale (English) as the most promising measures for those with CRC.