The analysis reviews time series data for the period 1945 to 1980 on media coverage and corresponding public attention to a set of ten political issues including poverty, racial problems, Watergate, and Vietnam. The study focuses on the early stages of public awareness and the need for a “critical mass” or threshold to move a matter from the status of private concern to a public, political issue. The pattern of evolving public awareness varies dramatically for different types of issues. In some cases, the public appears to have a much steeper “response function” in reacting to real-world cues than the media; in other cases, the media seem to be more responsive. Modeling the growth of attention to public issues with the logistic curve met with modest success. The article concludes with a call for much closer coordination between agenda-setting research and the study of political cognition.