摘要：The main objective of this research is to assess the existence （or lack） of media concentration in the Portuguese dailies newspaper sector, and to evaluate the extension to which this situation may be compromising fundamental society values： freedom of speech and right of access to information. Authors resorted to market indicators, namely total average circulation,number of copies per issue, business volume and advertising investments. These indicators are found to be complementary： some indicators evaluate group position in the readers＇ market, whereas other evaluates group position in the general market and the advertising market in particular. Based in this market information, we used quantitative models （HII, CR4 and Noan） to measure de concentration in the newspaper segment. Additionally we tried to demonstrate that to analyze the dailies newspaper concentration situation in Portugal a holist perspective of the media market is needed, using a country context to understand some local characteristics and market structure and political, economic, social and technological dynamics. Additionally, there are evidences that existing concentration indexes are not conclusive because of potential replacement effects in the Portuguese media sector.