The two volume set LNCS 14958 + 14959 constitutes the proceedings of the 15th International Conference of the CLEF Association, CLEF 2024, held in Grenoble, France, during September 9-12, 2024. The proceedings contain 11 conference papers; 6 best of CLEF 2023 Labs' papers, and 14 Lab overview papers accepted from 45 submissions. In addition an overview paper on the CLEF activities in the last 25 years is included. The CLEF conference and labs of the evaluation forum deal with topics in information access from different perspectives, in any modality and language, focusing on experimental information retrieval (IR). .