This book constitutes the refereed proceedings of the 11th International Workshop on Arithmetic of Finite Fields, WAIFI 2026, held in Santander, Spain, during June 3–5, 2026.

The 21 full papers and 3 Invited papers included in this book were carefully reviewed and selected from 31 submissions. They were organized in topical sections as follows: Invited talks; Coding Theory and Related Structures; Cryptography and Boolean Functions; Finite Field Arithmetic, Algorithms, and Implementations; and Combinatorics, Curves, and Dynamical Structures.