This book constitutes the proceedings of the 9th International Joint Conference on Rules and Reasoning, RuleML+RR 2025, held in Istanbul, Turkey, during September 22–24, 2025. The 12 full papers and 2 short papers included in this book were carefully reviewed and selected from 34 submissions. The proceedings also include 1 invited paper from a keynote speaker and 2 invited abstracts for keynotes. The 12 full and 2 short papers included in these proceedings were carefully reviewed and selected from 34 submissions. They focus on all subjects concerning theoretical advances, novel technologies, and innovative applications relating to knowledge representation and reasoning with rules.