###### Abstract  
Incineration bottom ashes (IBA) are the main waste from municipal solid waste (MSW) incineration. In the Iberian countries (Portugal and Spain), MSW incineration with energy recovery (WtE) plays an important role in MSW management. IBA is highly produced and managed differently both between and within countries. This paper aims to provide a comprehensive overview of the management model of IBA using the Iberian Peninsula as a case study, addressing its properties, current management, incentives and difficulties in valorizing, and prospects. For this purpose, incineration plants of both countries were approached, and a broad literature review was conducted to gather information. About 10% and 41% of IBA have been landfilled in Portugal and Spain, respectively. Metals (mostly ferrous) from Portuguese (6% of IBA) and Spanish (9% of IBA) WtE plants are recycled. In Portugal, the remaining IBA (84%) has been temporarily stored (11%), applied to landfills as a substitute for soil in intermediate and final covers, construction of paths, accesses, and platforms (41%), or used in civil engineering work and road construction (48%). In Spain, the remaining IBA (50%) has been reused mainly as a secondary raw material in the construction and civil engineering fields (77%), while the rest has been temporarily stored (11%), applied in the conditioning of landfills (4%), also secondary aggregate replacing natural materials. Both countries regulate IBA reuse outside landfills but consider different requirements and criteria. Nevertheless, there are both drivers and barriers to valorization. In the future, different IBA applications will likely continue to be developed, with the concern of protecting the environment. Growing confidence in IBA reuse following the publication of proper studies is expected. Globally, uniform legal frameworks among EU members with the same standards would likely lead to better IBA valorization. n 15 September 2021 11 October 202  
production has been increasing in the last few years up to about 5.3 Mt (513 kg per capita, higher than the EU average) in 2019 [5]. In 2018, Spain generated 22.3 Mt (486 kg per capita), close to the EU average [6], but still well above the targets set in the Spanish National Waste Management Plan 2016-2022 [7]. The heterogeneous and complex composition of wastes, along with their different origins and relationships with consumption patterns, create huge challenges for MSW management [8]. Currently, MSW incineration in waste-to-energy (WtE) plants is one of the main management strategies adopted in most developed countries. Although in Iberian countries this treatment is not as widespread as in Central Europe [9], MSW incineration with energy recovery has a key role in waste management, allowing the diversion of a significant fraction of wastes from landfills. Incineration in WtE plants decreases the volume and the weight of waste by about 90% and 70%, respectively [10; 11], and the energy may be recovered as electricity and/or heat. Nonetheless, MSW incineration creates new solid wastes, namely incineration bottom ashes (IBA) and air pollution control residues. IBA is the main solid output from the incineration process, accounting for about 80 wt.% of all incineration residues [12], and corresponds to the incombustible materials that remain in the furnace after combustion. IBA is produced worldwide, particularly, in Europe [13; 14], where around 18 Mt/year of IBA is generated [15]. The management methods currently applied to IBA are not uniform among European countries, where the strategies significantly diverge [15]. In this context, this paper aims at presenting the management model of IBA in the Iberian countries, namely Portugal and Spain, giving information on the properties of IBA, current management systems, motivations, and challenges for its valorization, and finally the expectations for the future in this regard.