What was the single most important marketing trend in the television business in the last decade of the 20 Century? Most of the dozens of professionals interviewed for this book seem to agree that segmentation was the keyword for any study on the television scenario. The purpose of this study, conducted in the early 1990s and still relevant as a historical document, is to review the development of television segmentation in the United States and its influence in the Brazilian industry, which was only recently going through a segmentation process.