In this article, we describe the usage of persuasion profiles in a large scale, N = 1,129, field trial. Persuasive technologies-technologies intentionally designed to influence user behavior-are emergent and becoming more and more individualized and ubiquitous. Individual differences in people's responses to often used persuasion principles-different psychological means by which to influence users-motivate personalization. We describe how, through identification, representation, and measurement, persuasive technologies can personalize their persuasive attempts. Next, we show that dynamically adapting a persuasive technology to the responses of its users increases the effectiveness of the system. Ubiquitous computing systems are, because of their ability to unobtrusively measure user behavior, very well suited for these types of applications.