This book constitutes the conference proceedings of 6th International Workshop on Algorithmic Bias in Search and Recommendation, BIAS 2025 and 2nd International Workshop on Information Retrieval for Understudied Users, IR4U2, held in Padua, Italy, on July 17, 2025.For BIAS 2025, 3 full papers were carefully reviewed and selected from 7 submissions. They focus on data preparation, countermeasure development, evaluation design, and case studies on algorithmic bias in search and recommendation.For IR4U2 2025, all 6 submitted full papers were carefully reviewed and accepted. They focus on user-centered artificial intelligence approaches aimed to better design, develop, and evaluate information retrieval systems that ensure true accessibility and inclusivity.