Technologists have been concerned about the privacy implications of online tracking systems for years. A Wall Street Journal series called What They Know brought widespread public attention to the issue by showcasing how marketers gather data on online users. Policy makers have begun devising ways to give users a choice about when they are tracked online. If you are concerned about who is tracking you and your family, you should become familiar with Do Not Track, a unique and powerful way of dealing with the problem of online tracking. It provides users with a voice for telling companies they do not want to be tracked online.