Retargeting has emerged as an effective way to improve results from Web marketing. Originally limited to serving Web banner ads to people who had previously visited a company’s Web site, it has now been expanded to include messages based on search terms, content viewed elsewhere on the web, and other online/offline behaviors. What these activities all share is insight into a person’s intent, which forms the basis for targeted advertising. Intent-based personalization and targeting is more effective than targeting based on demographics or the location an ad displays, older and still more common approaches. The trade-off is that intent is harder to identify, so audiences for retargeting messages are much smaller than those available using less refined methods.