This article focuses on Latvian contribution to European security, which, for the purposes of this study, is understood as a territorial system of regional security. Such system is a combination of interconnected institutions with Latvian participation operating in the field of security, Latvian cooperation with other European countries in the field of security, and the European perception of major security challenges and threats (that Latvia may or may not agree with). A systemic approach to studying the role of Latvia in the territorial system of European security requires a solid theoretical framework. The theories of international relations discussed in this article fall into two categories: those where territorial security systems are viewed as a product of external factors, and those that focus on internal regional factors. In this article, the authors rely on a variety of methods, including those that are characteristic of classical theories of international relations (such as realism and liberalism), and those employed in social constructivism studies. It is concluded that Latvian cooperation with institutions and countries of the territorial system of European security is rather limited, which indicates either a lack of the country’s integration into the system or a crisis of the system itself. An important result of the study is the validation of a systemic approach to studying regional security systems. This angle proves particularly useful in identifying crises of territorial systems of regional security in various regions of the world.