The Digital Markets Act is the european regulation EU 2022/1925 on contestable and fair markets in the digital sector which addresses the lack of contestability of core platform services, and imposes obligations on the undertakings designated as gatekeepers. In this article, we are going to introduce the key points of the Digital Markets Act: we start with contestability, what does it mean and the relation between the new discipline and competition law. We will then see what are the core platform services the regulation applies to, and when an enterprise qualifies to be designated as gatekeeper. Lastly: the Digital Markets Act mandates chat interoperability, between different providers of messaging apps. As this is meant to overcome the well known network effect, we will explain why it also poses risks for privacy and security.