The proliferation of regional economic organizations (REOs) is a prominent feature of the contemporary international environment. Many of these organizations aspire to promote regional peace and stability. Some strive to promote these goals only through economic cooperation, while others have expanded their mandate to include mechanisms that address security concerns more directly. A glance at the security components of such organizations indicates that their purpose and design are very diverse. This article sheds light on the sources of this poorly understood phenomenon. Specifically, it argues that organizations that enjoy greater delegated authority are in a better position to expand their mandate into the security realm and to have more far-reaching agreements in this issue area. It then develops a metric that gauges the degree of security cooperation within REOs and presents a new dataset of numerous organizations on this institutional aspect. Employing this dataset in a rigorous statistical analysis and controlling for a host of alternative explanations, it demonstrates that, indeed, REOs with greater delegated authority develop deeper security cooperation.