This chapter introduces a three-layer model designed to provide a structured understanding of regional “security architecture” in the Indo-Pacific. It commences with an effort to better define our terms of reference and dispel common misconceptions that surround the term. It then proceeds to outline layers I (multilateralism) and II (bilateralism), which have conventionally served as the two main pillars of regional security architecture. Within these layers it charts how the institutional landscape has empirically evolved from the prior “Asia–Pacific” into the “Indo-Pacific” epoch. This sets the stage for the examination of the newly-expanded layer II (minilateralism), which fills the space between these two existing ones (and which is treated separately in the following Chapter).