Running economy (RE) is the energy cost of running at a given speed, measured by oxygen consumption ($\dot{V}O_2$) and respiratory exchange ratio. Runners with better RE use less energy and oxygen at the same speed. RE is strongly linked to distance running performance, often more so than maximal oxygen uptake ($\dot{V}O_2max$) in elite runners with similar $\dot{V}O_2max$. RE is typically measured on a treadmill, though it may not perfectly reflect outdoor running. Standardization of testing conditions is crucial to ensure accurate results. Body mass (BM) must be considered when reporting RE, as $\dot{V}O_2$ does not increase linearly with BM. RE is influenced by physiological factors such as mitochondrial density, oxidative enzyme activity, and muscle stiffness, as well as biomechanical factors like flexibility and ground reaction forces. Interventions to improve RE include strength training, altitude exposure, and training in the heat. Strength training enhances elastic energy storage and reduces braking forces, while altitude exposure improves metabolic efficiency. RE is crucial for successful distance running, and future research should focus on methods to improve it. Efficient energy use is essential for endurance performance, with RE being a key factor. RE is measured as submaximal $\dot{V}O_2$ at a given speed and reflects the energy cost of running. Runners with better RE can achieve faster times at similar $\dot{V}O_2max$. RE can vary significantly among runners with similar $\dot{V}O_2max$, making it a better predictor of performance in elite runners.Running economy (RE) is the energy cost of running at a given speed, measured by oxygen consumption ($\dot{V}O_2$) and respiratory exchange ratio. Runners with better RE use less energy and oxygen at the same speed. RE is strongly linked to distance running performance, often more so than maximal oxygen uptake ($\dot{V}O_2max$) in elite runners with similar $\dot{V}O_2max$. RE is typically measured on a treadmill, though it may not perfectly reflect outdoor running. Standardization of testing conditions is crucial to ensure accurate results. Body mass (BM) must be considered when reporting RE, as $\dot{V}O_2$ does not increase linearly with BM. RE is influenced by physiological factors such as mitochondrial density, oxidative enzyme activity, and muscle stiffness, as well as biomechanical factors like flexibility and ground reaction forces. Interventions to improve RE include strength training, altitude exposure, and training in the heat. Strength training enhances elastic energy storage and reduces braking forces, while altitude exposure improves metabolic efficiency. RE is crucial for successful distance running, and future research should focus on methods to improve it. Efficient energy use is essential for endurance performance, with RE being a key factor. RE is measured as submaximal $\dot{V}O_2$ at a given speed and reflects the energy cost of running. Runners with better RE can achieve faster times at similar $\dot{V}O_2max$. RE can vary significantly among runners with similar $\dot{V}O_2max$, making it a better predictor of performance in elite runners.