A small number of large undertakings providing core platform services have emerged with considerable economic power that could qualify them to be designated as gatekeepers pursuant to this Regulation. Typically, they feature an ability to connect many business users with many end users through their services, which, in turn, enables them to leverage their advantages, such as their access to large amounts of data, from one area of activity to another. Some of those undertakings exercise control over whole platform ecosystems in the digital economy and are structurally extremely difficult to challenge or contest by existing or new market operators, irrespective of how innovative and efficient those market operators may be. Contestability is reduced in particular due to the existence of very high barriers to entry or exit, including high investment costs, which cannot, or not easily, be recuperated in case of exit, and the absence of, or reduced access to, some key inputs in the digital economy, such as data. As a result, the likelihood increases that the underlying markets do not function well, or will soon fail to function well.