Digitalization of content challenges legacy media products such as newspapers, and contributes to market exit and consolidation across geographical markets. Media market structures are changing continuously and the observation of increasing market concentration is not at all a new one. A meta-analysis of previous research on market and ownership concentration and its applications is presented. This chapter will also highlight some of the challenges in measuring and present the latest developments in assessing the effects of concentration of markets and ownership to central market outcomes. The final section concludes and discusses some remaining challenges in measuring concentration of markets and ownership.