The article examines how market power is defined and assessed in digital markets and its implications for competition policy. It highlights key sources of market power such as network effects, scale and scope economies, data advantages, and switching costs, and discusses whether these are unique to digital contexts. The note also reviews new concepts and regulatory terms used to describe power in digital markets and outlines policy challenges, including how new regulatory approaches relate to traditional concepts like dominance. It concludes that market power should remain a central principle in competition policy for the digital era.