The Cambridge Handbook of Behavioural Data Science offers an essential exploration of how behavioural science and data science converge to study, predict, and explain human, algorithmic, and systemic behaviours. Bringing together scholars from psychology, economics, computer science, engineering, and philosophy, the Handbook presents interdisciplinary perspectives on emerging methods, ethical dilemmas, and real-world applications. Organised into modular parts-Human Behaviour, Algorithmic Behaviour, Systems and Culture, and Applications―it provides readers with a comprehensive, flexible map of the field. Covering topics from cognitive modelling to explainable AI, and from social network analysis to ethics of large language models, the Handbook reflects on both technical innovations and the societal impact of behavioural data, and reinforces concepts in online supplementary materials and videos. The book is an indispensable resource for researchers, students, practitioners, and policymakers who seek to engage critically and constructively with behavioural data in an increasingly digital and algorithmically mediated world. Ganna Pogrebna is Professor at the University of Sydney Business School and lead of the Behavioural Data Science group at the Alan Turing Institute. She is a behavioural data science pioneer, author, educator, and expert in artificial intelligence and strategic decision-making. Her work explores how emerging technologies transform industries, customer experiences, and business models. She advises businesses and governments on AI adoption, innovation strategies, and building digital trust. Thomas T. Hills is Professor in the Department of Psychology at the University of Warwick. He studies how humans search, explore, and navigate complex environments across memory, decision-making, and creativity. His research integrates experiments, big data, network science, and AI to understand cognitive behaviour and societal evolution. He published widely on language, culture, and scientific communication. He is the author of Behavioral Network Science: Language, Mind, and Society (2024).