Study Design: Repeated-measures clinical measurement reliability study.Background: While there are some shoulder functional tests for athletes, no widely used performance test of arm and shoulder function currently exists to assess lower-level upper extremity functional demands in, for example, a nonathlete population or elderly individuals. In these individuals, functional measures rely on patient self-report.Objectives: Describe the development of the Timed Functional Arm and Shoulder Test (TFAST), age-related scores, and between-session reliability in a group of asymptomatic high school athletes, young adults, middle-aged adults, older adults, and a preliminary group of symptomatic patients.Methods: One hundred forty asymptomatic individuals participated in the study: 36 high school athletes (14–18 years of age), 34 young adults (19–35 years of age), 37 middle-aged adults (36–65 years of age), 33 older adults (over 65 years of age), and 16 symptomatic patients (22–66 years of age). The TFAST is a functional test that includes 3 tasks: hand to head and back, wall wash, and gallon lift. Total repetitions were noted for each task, and the total TFAST score was calculated.Results: Mean total TFAST scores were higher for young adults (107.9; 95% confidence interval [CI]: 102.5, 113.4) and middle-aged adults (105.2; 95% CI: 99.1, 111.3) as compared to the high school athletes (89.9; 95% CI: 81.2, 98.5) and older adults (74.5; 95% CI: 65.6, 83.5). All groups were significantly different (P<.05) from each other, except the young and middle-aged adults. For patients, the mean score for the symptomatic side was 100.1 (95% CI: 89.6, 110.5). The between-session reliability values for the total TFAST scores in the asymptomatic individuals were as follows: intraclass correlation coefficient (ICC) = 0.93; 95% CI: 0.60, 0.98; standard error of measurement, 6.7; and minimal detectable change based on a 95% CI, 18.5 repetitions. The ICC values for individual tasks ranged from 0.80 to 0.94 (95% CI range, 0.44–0.98). The reliability for the patient group was 0.83 (95% CI: 0.51, 0.94).Conclusion: The TFAST was sensitive to detect differences in functional performance between age groups, demonstrated adequate between-session reliability, and demonstrated feasibility in a symptomatic patient group. Further assessment is needed to refine the TFAST. Development of a feasible and valid test of arm function would enhance clinical evaluation and outcome measurement. J Orthop Sports Phys Ther 2017;47(6):420–431. Epub 3 Mar 2017. doi:10.2519/jospt.2017.7136