What would it take to achieve widespread and reliable information on carbon footprints of agri-food products? This report argues that eight building blocks are essential. Reporting standards, science-based methods, farm-level calculation tools, and databases with secondary data are needed to calculate carbon footprints, but these must be complemented with ways to communicate carbon footprint data along the supply chain, ensure the integrity and quality of the data and calculations, scale up carbon footprint calculations while keeping costs low, and to update all these elements as scientific insights and technologies evolve. Although the magnitude of the challenge should not be underestimated, this report shows that many of the building blocks are falling into place and can be improved and aligned through collaboration between researchers, farmers, other supply chain actors, governments, and civil society, both at domestic and international levels.