This LNCS book is part of the FOLLI book series and constitutes the proceedings of the 9th International Workshop on Logic, Rationality, and Interaction, LORI 2023, held in Jinan, China, in October 2023.The 15 full papers presented together with 7 short papers in this book were carefully reviewed and selected from 40 submissions. The workshop covers a wide range on the following topics such as agency; argumentation and agreement; beliefrepresentation; probability and uncertainty; belief revision and belief merging; knowledgeand action; dynamics of informational attitudes; intentions, plans, and goals; decisionmaking and planning; preference and utility; cooperation; strategic reasoning andgame theory; epistemology; social choice; social interaction; speech acts; knowledgerepresentation; norms and normative systems; natural language; rationality; philosophicallogic.