This book constitutes revised selected papers from International Workshops on AI Agent for Information Retrieval: Generating and Ranking, Agent4IR, taking place on October 25, 2024, in Boise, USA, and on March 4, 2025, in Pennsylvania, USA, and on August 3, 2025, in Toronto, Canada. The 12 full papers included in the book were carefully reviewed and selected from a total of 38 submissions. They focus on the latest theoretical advancements and practical implementations of AI agents in information retrieval, advance the field and enhance its societal impact.