This book constitutes the proceedings of the 21st International Symposium on Applied Reconfigurable Computing. Architectures, Tools, and Applications, ARC 2025, held in Seville, Spain, during April 9–11, 2025.

The 12 full papers presented in this book together with 1 short paper from the technical program were carefully reviewed and selected from 40 submissions.

ARC 2025 covers a wide range of topics, including hardware acceleration, security and fault tolerance, energy-efficient architectures, and emerging applications in artificial intelligence and high-performance computing. The symposium fostered collaboration and pushed the boundaries of state-of-the-art research.