Sustainable use of iron and steel lies on systematic comprehension and optimization of the anthropogenic cycle of iron flows and stocks. This study begins by characterizing contemporary iron flows through four fundamental life stages: production, fabrication and manufacturing, use, and waste management and recycling. The results of 68 countries and territories, nine world regions, and the planet as a whole demonstrate that current iron cycles are basically open and greatly dependent on environmental sources and sinks. In contrast to the relatively stable iron cycles in industrialized countries, the cycles in developing countries show high reliance on virgin minerals and strong potential of enhancement that is driven by the increasing need for material stocks to provide products in use. Case studies have thus been carried out for the two developing giants, India and China, with emphasis on stocks. Indian and Chinese in-use iron stocks have climbed to approximately 0.5 and 2.0 metric tons per capita as of 2005 and continue to increase. This pattern of iron stocks reflects the countries' rising demand for goods and services and diversified features of iron utilization in furnishing these products, presenting perspectives on forecasting the future iron use. The iron cycle is also compared with the cycles of other six metals (chromium, copper, lead, nickel, silver, and zinc) in China. This iron-based research offers unique insights into the policy and practice of iron-related resource management, industrial development, and waste and environmental governance.