This book constitutes the 4th 3D Head and Neck Tumor Segmentation in PET/CT Challenge, HECKTOR 2025, which was held in conjunction with the 28th International Conference on Medical Image Computing and Computer-Assisted Intervention, MICCAI 2026, on September 2025.The 15 full papers included in this book were carefully reviewed and selected from 15 submissions. They were organized in topical sections as follows: Tumor and Lymph Node Segmentation; Joint Learning: Segmentation with Prognosis and/or HPVPrediction; and Downstream Prediction from PET/CT and Clinical Data.
