Tagging, or using keywords to annotate images, bookmarks, and blogs, is gaining much popularity. Since tagging is seen as an important change in the way images are organized and shared, we need to understand what drives this behavior. We draw on taxonomy of individual-level motivations for tagging, and research on the impact of social presence on tagging, and examine the drivers of tagging. We develop a scale of tagging motivations, which distinguishes between motivations stemming from three categories of intended audience: the taggers themselves, their family and friends, and the general public. Using multiple sources, including a survey and independent system data, we find that the levels of the Self and Public motivations, as well as social presence factor are positively associated with tagging level, and that the family & friends motivation is not associated significantly with tagging level. Implications of the research are discussed.