Every year, new public health mass media campaigns are launched attempting to change health behavior and improve health outcomes. These campaigns enter a crowded media environment filled with messages from competing sources. Public health practitioners have to capture not only the attention of the public amid such competition, but also motivate them to change health behaviors that are often entrenched or to initiate habits that may be new or difficult. In what ways are public health mass media campaigns now attempting to succeed in a world crowded with media messages from a myriad of sources? What are the conditions that are necessary for a media campaign to successfully alter health behaviors and alter outcomes in the long term? To what extent can the successes and failures of previous campaigns be useful in teaching important lessons to those planning campaigns in the future? In this chapter we attempt to answer these questions, drawing from recent literature on public health mass media campaigns.