The opportunities and challenges to reducing industrial energy demand and carbon dioxide (CO2) emissions in the iron & steel sector are evaluated with a focus is on the situation in the United Kingdom of Great Britain and Northern Ireland (UK), although the lessons learned are applicable across much of the industrialised world. It is the largest industrial sector in the UK in terms of energy demand and 'greenhouse gas' (GHG) emissions, and accounts for some 26% of GHG emissions from British industry. Current Best Available Technologies (BAT) will lead to short-term energy and CO2 emissions savings in iron & steel processing, but the prospects for the commercial exploitation of innovative technologies by mid-21st century are far more speculative. The attainment of significant falls in carbon emissions over the period to 2050 will depend critically on the adoption of a small number of key technologies [e.g., energy efficiency techniques, fuel switching towards bioenergy, and carbon capture and storage (CCS)], alongside the decarbonisation of national electricity supply. The blast furnace is the most efficient energy conversion process in the sector, but also the largest energy user and consequently a priority target for energy demand reduction. Many existing technologies could reduce a significant proportion of process energy loss, e.g., heat recovery at the coke ovens, sinter plant, and electric arc furnace, and further heat and gas recovery from the basic oxygen furnace. The uptake of key BAT technologies for hot-rolling could reduce sector primary energy by 18% and GHG emissions by 12%. Further potential may be available for blast furnace operation by optimising chemical transfer to minimise blast furnace gas (BFG) production. Nevertheless, there are a number of non-technological barriers to the take-up of such technologies going forward. Other radical process technological innovations (such as the 'electrowinning' or so-called HISARNA process) are likely to be available in the longer term.