This book constitutes the proceedings of the 4th International Workshop on Advances in Simplifying Medical UltraSound, ASMUS 2023, held in conjunction with MICCAI 2023, the 26th International Conference on Medical Image Computing and Computer-Assisted Intervention. The conference took place in Vancouver, BC, Canada, on October 8, 2023. The 19 papers presented in this book were carefully reviewed and selected from 30 submissions. They were organized in topical sections as follows:​ advanced imaging, segmentation, and ultrasound techniques; predictive analysis, learning, and classification; multimodal imaging, reconstruction, and real-time applications; diagnostic enhancements and novel ultrasound innovations.