<p>Ferrous slag is the most abundant solid by-product generated from the steel manufacturing process, and a stable demand for ferrous slag is essential to ensure the stable production of steel. Therefore, various applications have been developed to maintain a stable demand for ferrous slag. Furthermore, continuous fundamental study and technological development are essential to find more value-added valorization and explore more advanced ways of use. It is inevitable to develop ideal slag valorization methods corresponding to new types of ferrous slag with a society-wide perspective to ensure the rapid decarbonization trend, which is an unprecedented experience in the steel industry. This article provides an overview of the progress and technological structure of ferrous slag valorization in Japan so far and also summarizes the research activities related to ferrous slag in recent years in the Iron and Steel Institute of Japan, which plays a central role in this field. Particularly, unique activities such as exploring environmentally friendly valorization methods using ferrous slag through collaboration between different industries such as agriculture and fisheries, and carbon fixation through vegetation promotion in coastal areas in Japan, harvesting blue carbon, are summarized. Based on the above, the future role of ferrous slag in establishing a sustainable society has been discussed.</p> Graphical Abstract <p></p>