Forty years ago in Chapel Hill, North Carolina, the first agenda-setting study showed that the issue priorities of the news become the issue priorities of the public in the 1968 U.S. presidential campaign. Since then, the agenda-setting model has been replicated in more than 400 studies that include both election and non-election settings, covering a wide variety of issues, and extending beyond the U.S. to a broad range of countries in the five continents. This article examines the progress of this research to date, reviewing its principal variations, how now encompasses five different theoretical stages, and what are the possible new areas of application and development.