A nudge is a small, subtle incentive or nudge given to an individual or consumer to modify their behavior. These “nudges” are a response to the observation that individuals often lack rationality, explained by various biases identified in the field of decision-making. An incentive nudge can take the form of a written message or a simple symbol. Among the most emblematic examples of these gentle incentives are: painted flies in urinals, visual cues designed to reduce speed at city entrances (distinct from speed limit signs), and messages encouraging hotel guests to reuse their towels and sheets. The work that popularized the concept of the nudge is that of Thaler and Sunstein. In this approach, gentle incentives are primarily used to encourage individuals to adopt beneficial behaviors, both individually and collectively, whether related to health, the environment, or road safety. The authors consider the use of nudging as a form of “liberal paternalism.” Elements of the nudge principle can be found in the field of social marketing (see this concept for concrete examples of nudge use). A typical approach to implementing a nudge (idea generation, experimentation, evaluation, etc.) shares similarities with an advertising communication approach using billboards. For example, using nudges to influence behavior in train stations is a concrete application of this concept. For more information on nudges, refer to the seminal work on this subject.