PALMS (Physical Activity Lifelong Modelling & Simulation) is an agent-based micro-simulation that predicts the lifelong physical activity behavior of individuals of a population and its effect on their quality of life. The simulation can be used to provide evidence of the cost-effectiveness of physical activity interventions. Using an individual’s characteristics it assesses how their physical activity and relative risk of various health conditions change over time. Health conditions currently include cardiovascular disease (CVD), diabetes, depression and musculoskeletal incidents (MSI). PALMS can also output information on the related costs of these conditions for a population.