HOOP Hub of Circular Cities Boosting Platform to Foster Investments for the Valorisation of Urban Biowaste and Wastewater EU Member States produce between 118 and 138 million tonnes of municipal biowaste annually*. Of this biowaste, only around 40% is recycled, highlighting both the scale of the challenge and the opportunity to improve and innovate biowaste management systems across Europe. Biowaste, defined as waste of organic origin such as manure, sawdust, or food scraps, represents the single largest fraction of municipal waste generated each year in the EU. A significant share of this biowaste still ends up in landfills or is incinerated, leading to the loss of valuable resources. Existing circular solutions, including composting, digestate use, and biogas production, demonstrate that more circular approaches are already feasible. At the same time, the potential for biowaste recovery extends well beyond these established pathways. Against this backdrop, the HOOP project addressed the challenge of biowaste valorisation by supporting the development of local bioeconomies and fostering investments through a systemic and cross-cutting approach. The project focused on creating and testing innovative biowaste valorisation routes and value chains in selected European cities and regions, referred to as “lighthouses”. The lighthouse cities and regions involved in the project were Bergen (Norway), Kuopio (Finland), Almere (Netherlands), Münster (Germany), Albano Laziale (Italy), Kozani in Western Macedonia (Greece), Murcia (Spain), and Porto (Portugal). Across these locations, technical solutions for biowaste valorisation were implemented and assessed, while experiences and lessons learned were exchanged within the project and shared with follower cities and regions. Given the diverse cultural contexts and the varying legal, socio-economic, environmental, and geographical conditions of the lighthouse regions, stakeholder engagement played a crucial role in the project. The Collaborating Centre on Sustainable Consumption and Production (CSCP) led the work package on stakeholder engagement. The CSCP coordinated engagement activities across the project, involving public authorities, private companies along relevant value chains, and actors from civil society. A central instrument for this work was the establishment of so-called Biowaste Clubs, which served as structured yet flexible platforms for dialogue and collaboration at local level. While the CSCP supported the overall coordination and methodological framing of the Biowaste Clubs, responsibility and ownership were placed with local partners and stakeholders, allowing engagement formats to be adapted to local needs and contexts. In addition to facilitating stakeholder collaboration, the stakeholder engagement work package aimed to support knowledge development and behavioural change among stakeholders and consumers. This included addressing issues such as improved biowaste separation practices and acceptance of bio-based products resulting from new valorisation pathways. The HOOP project built on and exchanged closely with three related Horizon 2020 projects: SCALIBUR, ValueWaste, and WaystUP. In particular, CSCP drew on experience from the SCALIBUR project when designing and implementing stakeholder engagement activities within HOOP. HOOP was funded under the European Union’s Horizon 2020 research and innovation programme and ran from 2020 to 2025. The consortium consisted of 23 partners from across Europe. *European Compost Network 2019