Tradition measures of recovery, such as patient-reported symptoms, objective measures such as balance, specific dimensions such as depression, fatigue, cognitive status, and exercise tolerance do not fully capture the impact of the concussion on performing individual activities and participating in life situations as experienced by the patient. No concussion-specific measure of functional status currently exists. Objectives The overarching purpose of this dissertation was to develop a concussion-specific measure of functional status. There were two specific objectives: 1. To examine the concept of functioning post-concussion; 2. To generate questionnaire items based on a conceptual model of functioning. Methods This dissertation follows the recommendations of the Association for Medical Education in Europe as a framework with which to meet the objectives. The first objective was addressed by (1) generating a list of concussion-specific concepts through a systematic review (Chapter 3), and (2) qualitative interviews with individuals with persistent post-concussion symptoms and clinicians with concussion expertise (Chapter 4). The relationships between the concepts that emerged from those studies are presented graphically in a conceptual model to meet the second objective. The concepts were then transformed into questionnaire items and pretested through cognitive interviews with individuals with PPCS and clinicians with concussion expertise. Finally, the questionnaire items were critically evaluated for proportion of shared content against existing measures used in concussion clinical trials by coding all items to the International Classification of Functioning, Disability and Health. Results Objective 1 Three main themes emerged from the qualitative findings: (1) functioning at the level of the individual and society; (2) environmental barriers and facilitators; and (3) capacity, defined as the length of time one could perform a task before the onset of symptoms, and the length of time it took to recovery from those symptoms. Objective 2 The final questionnaire is presented as the CORE-Q, which is comprised of 53 items over three complimentary subscales, namely the Post-Concussion Functional Scale, the Concussion Modifiers Scale, and the Global Functional Recovery Scale. Each subscale corresponds to one of the three main themes. No existing outcome measure contained more than 40% of the content within the CORE-Q, or 55% of any subscale. Conclusions The CORE-Q is a unique measure of functional status post-concussion that considers functioning from a biopsychosocial perspective. Further studies are needed to assess the psychometric properties of the CORE-Q before it is adopted into clinical practice and intervention trials.