Cyberspace presents a new arena for international relations and order. As society becomes more reliant on this domain it increases vulnerabilities against cyber threats. While the EU and NATO have been long-time partners in security and defence within traditional domains, this thesis aims to explore how we can understand EU-NATO cooperation within cyberspace with regards to cyber security and defence. Previous literature has mainly focused on their shared membership and their efforts to avoid duplication. This thesis aims to contribute to the field by providing a critical lens to this partnership in cyberspace. Through a combined critical theoretical framework that centers the impact of technologies on society, this thesis argues that their partnership is representative of the larger phenomena of blurring the lines between pre-existing parameters between military and civilian, thus allowing for maneuvering that would otherwise be contested, and to reinforce a liberal order in cyberspace. This thesis combines Critical Security Studies, Critical Military Studies and Science and Technology Studies to conduct theory driven discourse analysis on EU and NATO discourse to analyze how we can think about their partnership in cyberspace. Expert interviews are used in this thesis not as a core methodological approach, but rather as additions that help color the analysis. This thesis argues that while shared membership and EU-NATO efforts to avoid duplication is a large part of their cooperation efforts, this cooperation goes beyond convenience. The analysis finds that the EU and NATO do not conceptualize cyberspace and cybersecurity the same way, nor do they perceive the referent object within cyberspace the same. However, I argue that it is precisely due to their diverging conceptualizations that cooperation is mutually beneficial. As this thesis will illustrate, their cooperation blurs the lines between military and civilian, thus allowing each actor room to maneuver into conceptualizations of security and cybersecurity they would otherwise not have had the opportunity to explore. Lastly, this thesis illustrates that EU- NATO cooperation is part of a larger contestation within cyberspace to impose a liberal order through the values and norms they export into this domain. Therefore, it examines how cyberspace and cybersecurity influence EU and NATO, and in reverse how NATO and EU influence this new arena to establish a liberal order.