This book constitutes the refereed proceedings of the 12th International Conference on Health Information Science, HIS 2023, held in Melbourne, VIC, Australia, during October 23–24, 2023. The 20 full papers and 9 short papers included in this book were carefully reviewed and selected from 54 submissions. They were organized in topical sections as follows: Depression & Mental Health, Data Security, Privacy & Healthcare Systems, Neurological & Cognitive Disease Studies, COVID-19 Impact Studies, Advanced Medical Data & AI Techniques, Predictive Analysis & Disease Recognition, Medical Imaging & Dataset Exploration, Elderly Care and Knowledge Systems.