The International Open and User Innovation (OUI) Conference is the leading academic conference on user innovation and open innovation, two closely related paradigms that have changed our thinking about innovation and creativity in the last decades. Organized by the Open & User Innovation Society since 2002, the OUI Conference brings together about 300-400 researchers from around the world to exchange recent research in open innovation, user innovation, open source/open hardware, collaborative innovation, citizen/free innovation, open innovation policies, and related topics. In 2021, the Institute for Technology & Innovation Management at RWTH Aachen University, Germany, hosted the 18th edition of this conference. The community of scholars meeting at OUI is characterized by a very open, developmental academic culture sharing plenty of feedback and ideas. The conference targets mainly an academic audience of faculty, senior researchers, and PhD students, but is also open to reflected practitioners and policy makers interested in open and user innovation. The OUI is truly multidisciplinary, covering disciplines such as innovation management, strategic management, organization design, marketing, intellectual property rights, entrepreneurship, and public policy, but also health care, psychology, and industrial engineering and design. In the center of the conference are its academic tracks, presenting both latest research (full presentations) and research ideas & proposals – hence providing a glimpse into the future of OUI: Open Social Innovation: Healthcare, Sustainability, and Societal Challenges; Open and User Innovation Platforms; Lead users, Toolkits, and User Identification; Firms‘ Capabilities and Interaction for Open and User Innovation; Crowdsourcing and Distributed Problem Solving; Crowdfunding and User Entrepreneurship; Institutions, Innovation Law, and Policy; Open Software, Open Hardware, and Makers; Diffusion of Open and User Innovation; The Internet of Production: Industry 4.0, User Process Innovation, and Data Ecosystems.