This chapter establishes the robust theoretical foundation essential for analyzing the complex operational dynamics of Track 1.5 Diplomacy. It systematically grounds the study within the dominant paradigms of International Relations (IR) theory: Realism, Liberalism, and Constructivism. Realism offers a foundational understanding by emphasizing the anarchic nature of the international system and states’ pragmatic, self-interested pursuit of power, framing Track 1.5 Diplomacy as a tool for “soft-balancing” and gathering intelligence rather than genuine cooperation. Conversely, Liberalism provides an optimistic lens, highlighting the critical role of non-state actors, economic interdependence, and international institutions in fostering dialogue, thereby positioning Track 1.5 Diplomacy as a natural extension of liberal principles and institutionalized cooperation. Constructivism introduces a crucial third dimension, arguing that ideas, norms, and shared identities fundamentally shape state behavior, explaining how unofficial channels are instrumental in building the social fabric and security communities necessary for long-term peace. Furthermore, the chapter explores the influence of Transnational Advocacy Networks (TANs) and concludes by advocating for an Analytic Eclecticism—a multi-paradigmatic approach—to integrate the strengths of these competing theories. This synthesis provides a comprehensive and nuanced framework necessary to fully capture the multifaceted mechanisms, motivations, and outcomes of hybrid diplomacy in contemporary global affairs.