Platform power is a societal concern on many levels. Thus, we argue that addressing it with the common market competition approach is limited. The research we present aims to develop and test an alternative approach to conceptualising and assessing platform power. We propose a framework that operationalises the concept of the integrated platform ecosystem by bounding it with theories of harm to citizen wellbeing. Applying it, instead of defining a market, we use a specific, novel theory of harm to define the audiovisual advertising ecosystem. Our investigation into the dynamics of this ecosystem and conditions shaping them incorporated elite interviews with representatives of firms involved, document analysis and an examination of legal frameworks in a sample of four European jurisdictions. The evidence we present points to an inherent bias in the opacity of trading and to systemic advantage in relationship building, as well as potential power imbalances at 'nodes' where data is used for targeting, planning, and metrics. We discuss the policy implications of these findings and suggest specific questions for regulators to be asking. Issue 4 1. The European Commission's Directorate General for Competition has fined both Facebook and Google following recent investigations (see European Commission 2017a, 2017b & 2019) and in autumn 2019 US State Attorney Generals formally launched antitrust investigations into Facebook and Google's parent company Alphabet (see Paxton, 2019; James, 2019), followed shortly after by the US Department of Justice.