This book constitutes the refereed proceedings of the 21st International Conference on Virtual Reality and Mixed Reality, EuroXR 2024, held in Athens, Greece, during November 27-29, 2024. The 14 full papers presented together with 1 short paper were carefully reviewed and selected from 47 submissions. The papers are grouped into the following topics: Designing Experiences, Human Factors, Rendering and Visualization, Interaction Techniques, and Education and Training. EuroXR aims to foster engagement between European industries, academia, and the public sector, to promote the development and deployment of XR tech niques in new and emerging, but also in existing fields.