The chapter provides a conceptual overview on the notion of infrastructure in international relations with a particular focus on the maritime domain. It explores how these infrastructures shape socio-political dynamics and influence geopolitical strategies on multiple levels. By analyzing the material, agential, and ideational properties of infrastructure, the chapter highlights the strategic significance of these systems in global geopolitics, particularly as targets of hybrid threats. Using case studies and theoretical insights, this chapter provides a comprehensive understanding of CMI as both a foundational asset and a strategic instrument within the complex landscape of international security.