Unhealthy diet plays a role in 11,000 deaths each year in New Zealand, and healthier diets are important in preventing common diseases like heart disease, stroke, cancer, and diabetes. Supporting people to make healthier food choices has important health benefits. This research will assess the impact of promising ways to improve diets including: (1) introduction of simple front-of-pack nutrition labels; (2) changes in food prices (making healthy foods cheaper and unhealthy foods more expensive); (3) changes to the composition of foods to reduce salt and saturated fat; and (4) restriction of food marketing to children. These approaches are difficult to implement and evaluate in everyday life so we will use leading-edge technologies to test interventions and measure their effects on diets and long-term health. Our research will provide vital information directly relevant to national and international policies on the most effective and cost-effective ways to improve population diets and health.