Advertising and marketing are intimately associated with modern society; in 2015, the total cost of advertising in Sweden amounted to over SEK 68 billion or 1.6 percent of Sweden's GDP. Research on the historical roots of advertising is extensive, both in Sweden and internationally, but there has been a great lack of source material from the advertising industry which has limited previous studies. The project "För reklamens bästa. The Swedish advertising industry, the daily press and the battle for the advertising market 1915-1965" has gained access to a new and extensive source material, which provides a unique opportunity to study the development of the advertising industry over a long period of time and answer research questions that were previously impossible to answer. While the development covers several aspects of business history, the project will focus on investigating a long-standing cartel in the advertising industry that was based on close cooperation between the largest advertising agencies and the newspapers. The cartel, which is unique from an international perspective, shaped the advertising market for five decades. How the cooperation worked, how it was legitimized and also what effects it had, especially for the development of the advertising industry in Sweden, are the main research questions. The project will provide an important contribution to the Swedish advertising history research and also to the international research on cartels, which in principle lacks studies from the service and knowledge sector.