Walking speed (WS) is a valid, reliable, and sensitive measure used to assess and monitor functional status and overall health in various populations. It has been designated as the "sixth vital sign" due to its predictive capabilities for outcomes such as rehabilitation response, functional dependence, frailty, mobility disability, cognitive decline, falls, institutionalization, hospitalization, cardiovascular events, and mortality. WS is also associated with lower quality of life, decreased participation, and depressive symptoms. WS tests are applicable in both clinical and research settings and can be used to monitor changes over time. WS tests can be performed in various settings and are suitable for a wide range of diagnoses. They are responsive to changes in WS over time and can be used to assess both self-selected and maximal walking speeds. The minimal detectable change (MDC) values for WS are provided for different populations and settings. WS tests are typically conducted over a distance of 5 to 10 meters, with an acceleration phase of approximately 2.5 meters for self-selected speeds and 3.25 meters for maximal speeds. A straight path is recommended to capture steady-state walking speed. WS tests can be conducted using stopwatches, automatic timers, or instrumented walkways. While instrumented walkways provide more accurate results, they are less clinically feasible due to cost. Stopwatches and marked walkways are more practical and reliable alternatives. Clinicians should maintain consistency in testing procedures to ensure accurate conclusions. WS tests can guide clinical decision-making by identifying individuals at risk of adverse outcomes. WS is influenced by multiple factors, including posture control, lower extremity strength, aerobic capacity, proprioception, and vision. Patients with impaired WS should undergo further testing to determine the cause of their decreased speed. WS remains a valuable tool for assessing and monitoring health in various populations. It is a simple assessment that provides comprehensive information about underlying physiological processes and is cost-effective. Clinicians should incorporate WS into all comprehensive evaluations.Walking speed (WS) is a valid, reliable, and sensitive measure used to assess and monitor functional status and overall health in various populations. It has been designated as the "sixth vital sign" due to its predictive capabilities for outcomes such as rehabilitation response, functional dependence, frailty, mobility disability, cognitive decline, falls, institutionalization, hospitalization, cardiovascular events, and mortality. WS is also associated with lower quality of life, decreased participation, and depressive symptoms. WS tests are applicable in both clinical and research settings and can be used to monitor changes over time. WS tests can be performed in various settings and are suitable for a wide range of diagnoses. They are responsive to changes in WS over time and can be used to assess both self-selected and maximal walking speeds. The minimal detectable change (MDC) values for WS are provided for different populations and settings. WS tests are typically conducted over a distance of 5 to 10 meters, with an acceleration phase of approximately 2.5 meters for self-selected speeds and 3.25 meters for maximal speeds. A straight path is recommended to capture steady-state walking speed. WS tests can be conducted using stopwatches, automatic timers, or instrumented walkways. While instrumented walkways provide more accurate results, they are less clinically feasible due to cost. Stopwatches and marked walkways are more practical and reliable alternatives. Clinicians should maintain consistency in testing procedures to ensure accurate conclusions. WS tests can guide clinical decision-making by identifying individuals at risk of adverse outcomes. WS is influenced by multiple factors, including posture control, lower extremity strength, aerobic capacity, proprioception, and vision. Patients with impaired WS should undergo further testing to determine the cause of their decreased speed. WS remains a valuable tool for assessing and monitoring health in various populations. It is a simple assessment that provides comprehensive information about underlying physiological processes and is cost-effective. Clinicians should incorporate WS into all comprehensive evaluations.