Proceedings of the 3rd Italian Conference on Big Data and Data Science (ITADATA2024), held in Pisa, Italy, September 17-19, 2024. The Italian Conference on Big Data and Data Science (ITADATA2024) is the annual event supported by the CINI Big Data National Laboratory and ISTI CNR that aims to put together Italian researchers and professionals from academia, industry, government, and public administration working in the field of big data and data science, as well as related fields (e.g., security and privacy, HPC, Cloud). ITADATA2024 covered research on all theoretical and practical aspects of Big Data and data science including data governance, data processing, data analysis, data reporting, data protection, as well as experimental studies and lessons learned. In particular, ITADATA2024 focused on - Data spaces - Data processing life cycle - Machine learning and Large Language Models - Applications of big data and data science in healthcare, finance, industry 5.0, and beyond - Data science for social network analysis