This open access book constitutes the proceedings of the First International Workshop on Migration and Agility in Cryptographic Systems, MAgiCS 2026, which took place on May 20, 2026, co-located with Eurocrypt 2026.

The 10 full papers included in this book were carefully reviewed and selected from 19 submissions. MAgiCS 2026 focuses on the topic of migration and the transition of cryptographic systems. The workshop aims to bridge the gap between theoretical concepts and practical processes for their application in real-world scenarios.