This book constitutes the proceedings of the 9th International Conference on Decision Support Systems Technologies, ICDSST 2023, held during May 30 - June 1, 2023. The EWG-DSS series of International Conference on Decision Support System Technology (ICDSST) is planned to consolidate the tradition of annual events organized by the EWG-DSS in offering a platform for European and international DSS communities, comprising the academic and industrial sectors, to present state-of-the-art DSS research and developments, to discuss current challenges that surround decision-making processes, to exchange ideas about realistic and innovative solutions, and to co-develop potential business opportunities. The main theme of this year was "Decision Support Systems in An Uncertain The Contribution of Digital Twins".The 21 papers presented in this volume were carefully reviewed and selected from 65 submissions. They were organized in topical sections as DSS models, methods, and tools; DSS for business performance and stakeholders; DSS applications for sustainability in health, energy and transportation; and DSS users and successful adoption.