This book investigates behaviour change technologies (BCTs) from an ethical perspective, examining the broader societal and philosophical implications of these types of technologies. These technologies-ranging from fitness trackers and smart home systems to digital nudging and persuasive AI-are increasingly shaping our choices, habits, and lifestyles. This book moves beyond nudging and persuasion to explore a broader spectrum of ethical concerns, including autonomy, privacy, trust, responsibility, and social justice. Contributors from leading scholars do not merely critique BCTs but also offer constructive ethical frameworks and ethical analysis for their responsible design and implementation.