To define the appeal of museums, historic sites, and other informal learning settings, one must understand the feeling component of the experience, not just the informational one. This article seeks to clarify the nature of this affective factor, especially as it can be distinguished from the larger term emotion. The origin of affect in personal relevance and its more specific sources in identification, human interest, and stimulus characteristics are discussed. The role that affect plays in directing attention, aiding memory, and allowing decision making are explored relative to its use in exhibits and displays. Finally, a simple method of measurement is introduced to encourage its assessment for improvement of informal learning and its use in research.