The IEEE International Conference on Software Architecture (ICSA) is the premier gathering of practitioners and researchers interested in software architecture, component-based software engineering, and quality aspects of complex software systems. The 21st IEEE International Conference on Software Architecture (ICSA 2024) continued the tradition of a working conference, where attendees met and where software architects were able to explain the challenges they face and try to influence the future of the field. Interactive working sessions were the place where researchers met practitioners to identify opportunities to shape the future of our field.