This book constitutes the refereed proceedings of the third MICCAI challenge on Mitosis Domain Generalization (MIDOG), addressing WSI-level mitotic figure detection and atypia classification, held in conjunction with MICCAI 2025, in Daejeon, South Korea, on September 23, 2025.The 8 full papers and 20 short papers presented in this volume were carefully reviewed and selected from 32 submissions.  They are grouped into the following topics: Extended Papers; Short Papers for Track 1 (Mitotic Figure Detection); Short Papers for Track 2 (Atypia Classification); and combined Short Papers for Track 1 and 2