This book constitutes the Third International Challenge on Kidney and Kidney Tumor Segmentation, KiTS 2023, which was held in conjunction with the 26th International Conference on Medical Image Computing and Computer-Assisted Intervention, MICCAI 2023. The challenge took place in Vancouver, BC, Canada, on October 8, 2023. The 22 contributions presented in this book were carefully reviewed and selected from 29 submissions. This challenge aims to develop the best system for automatic semantic segmentation of kidneys, renal tumors and renal cysts.