Can a large-scale social media platform decide to block access to legal content? The question on who gets to decide what content can and what content cannot be posted on social media platforms is closely intertwined with the question what social media platforms are and how they fit into the existing legal framework. However, consensus on the definition of social media platforms has not (yet) been achieved - neither in the academic literature nor in legal practice.

This article demonstrates how subtle differences in the definition of social media platforms have led to an incoherent European system to address content restrictions on social media platforms. Departing from the definition of social media platforms in three European Member States (Denmark, Germany, and the Netherlands), the article uncovers that, recently, national courts have taken a normative stance on the definition of social media platforms. However, the definitions differ from one Member State to another, creating a patchwork of applicable laws across the European Union.

Following this contextualization in European national case-law, the article continues with a literature review to summarizes the various views on the qualification of online platforms in the literature. The study uncovers six main qualifications: services of general interest, universal services, essential facilities, publicly owned public spaces, privately owned public spaces, and public spheres. Subsequently, the author assesses the viability of these different qualifications and concludes that social media platforms cannot be qualified as services of general economic interest, essential facilities, or publicly owned public spaces. Finally, the other three viable qualifications are examined in detail. Inspired by the German Bundesgerichtshof, the author proposes to qualify social media platforms as privately owned public spaces with a spectrum of procedural rules related to how ‘general’ the platform has opened its service.