This book constitutes the proceedings of the 21st International Conference on Mobile and Ubiquitous Systems: Computing, Networking and Services, MobiQuitous 2024, held in Oslo, Norway, during November 12–14, 2024.The 32 full papers presented in this book were carefully reviewed and selected from 73 submissions. They were organized into the following topical sections: Health, Biomedical Applications, and Human-Centric Computing; IoT, Cybersecurity, and Wireless Communication; Machine Learning, AI, and Smart Systems; Robotics and Autonomous Systems; and Simulation, Optimization, and Specialized Techniques.