This LNCS volume constitutes the proceedings of 12th International Conference, GALA 2023, in Dublin, Ireland, held during November/December 2023. The 36 full papers and 13 short papers were carefully reviewed and selected from 88 submissions. The papers contained in this book have been organized into six categories, reflecting the variety of theoretical approaches and application domains of research into serious games: 1. The Serious Games and Game Design 2. User experience, User Evaluation and User Analysis in Serious Games 3. Serious Games for Instruction 4. Serious Games for Health, Wellbeing and Social Change 5. Evaluating and Assessing Serious Games Elements 6. Posters.