The book investigates the concept of platform as a market player and identifies specific platforms' characteristics that make it practical from the competition law enforcement point of view to distinguish between leveraging practices that extend a market power from one platform to another and ones that are implemented to the same effect between the two sides of the same platform. The book finds that differential treatment by competition law enforcement is justified as soon as the type of connection between the markets is taken into account. To prove this point the book juxtaposes the abusive behaviour in Google (Shopping) and Google (Android) cases that resemble each other in any way other than the type of connection between the markets involved. By matching the elements of the conduct with the full range of available formal tests developed in the settled case law on market power leveraging the book demonstrates the weaknesses of various formal classifications of the behaviour in question under art. 102 TFEU highlighting the edges of the associated enforcement gap. The book argues that the latter can be effectively tackled by incorporating the analysis of the connections between the relevant markets into the formal leveraging tests. It further outlines three main routes the CJEU may take to implement the change.