MUM 2022, the 21st International Conference on Mobile and Ubiquitous Multimedia will be held in Lisbon, Portugal, November 27th - 30th. MUM is an interdisciplinary forum for advances in research of mobile and ubiquitous multimedia systems, applications, and services. At MUM, academics and practitioners gather to discuss challenges and achievements in this field from diverse perspectives, such as interaction techniques, user research, system development, software solutions, and devices. This edition of MUM aims to continue the tradition of innovation and excellence in research established by previous MUM conferences. We welcome high-quality submissions to a wide range of tracks dealing with, among others, the following topics: - Architectures, systems, algorithms and other constructions tackling relevant technical challenges - Augmented, mixed, and virtual reality systems and applications - Case studies, field trials, or user experience evaluations of new applications and services - Conceptualizations and theorizations of the field - Context-aware and location-based mobile and ubiquitous services - Metrics and measures for evaluating and testing mobile and ubiquitous systems - Middleware and distributed computing support for mobile and ubiquitous multimedia - Novel applications for mobile and ubiquitous gaming, entertainment, networking, and advertising - Privacy and security related issues to multimedia systems - Social implications of mobile and ubiquitous multimedia systems - Tools and development environments for building mobile, wearable, and ubiquitous multimedia systems - User interfaces, interaction design, and interaction techniques for mobile and ubiquitous systems Our tracks have the following submission deadlines (extended) (all AoE) - Posters, Demos, and the Doctoral Consortium: October 7, 2022 Accepted posters and demos will appear in the Proceedings of the International Conference on Mobile and Ubiquitous Multimedia, which will be available in the ACM Digital Library. For further details on each individual track, please visit https://mum-conf.org/2022/ We hope to see you all at MUM 2022 in Lisbon, Portugal, João Guerreiro, LASIGE, ULisbon Augusto Esteves, ITI / LARSyS, ULisbon