Global food security remains an elusive goal despite decades of advances in agriculture and nutrition. Food systems around the world have made substantial progress since the 1960s, when expanded yields across Asia drove growth of the global food supply. Today the world produces food in excess of per capita energy needs but still does not meet nutrient- or food-based benchmarks for healthy diets. Even when healthy diets are available in local marketplaces, high food prices and low incomes mean that healthy diets are unaffordable to consumers in many parts of the world. This chapter provides an overview of evolving definitions of food availability and access to healthy diets, progressing from energy and nutrient adequacy to the availability and economic accessibility of healthy diets. New food access metrics use retail food price data to measure economic access to nutritious and healthy diets around the world, while historical food supply data provide insights into the availability of healthy diets over time. Taken together, these metrics indicate that while world food systems have progressed toward closer alignment with dietary guidelines for human health, there are important shortfalls that remain for the availability and economic accessibility of healthy diets. These metrics have emerged as important new tools in the effort to reduce global hunger and malnutrition while improving long-term quality of life.