Hydrogen demand is already strong. it should significantly increase in the next few years due to the refinery industry's growing needs and new applications such as synthetic fuel or biofuel production. To meet the demand, advanced processes are being developed throughout the world in a sustainability, context. Among the most studied ones are thermochemical cycles: the sulphur-iodine and hybrid-sulphur cycles. For each of these processes, a thorough study was carried out from the flowsheet development to the final hydrogen production cost assessment, through the sizing and costing of the equipment, providing some insights about the process economic competitiveness given the current state of knowledge. This paper presents the analysis conducted for the sulphur-iodine cycle, which leads to a hydrogen production cost around 12 (sic)/kg. The main contributions to that cost are discussed. (C) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.