One of Chinese president Xi Jinping's signature foreign policy programs is the Belt and Road Initiative (BRI), a web of infrastructure development plans designed to increase Eurasian economic integration. Chinese official rhetoric on the BRI focuses on its economic promise and progress, often in altruistic terms: all countries have been invited to board this "express train" to wealth and prosperity. Missing from the rhetoric is much discussion of the initiative's security dimensions and implications. Chinese officials avoid describing the strategic benefits they think the BRI could produce, while also gliding over major security risks and concerns. Yet at the unofficial level, China's security community has paid close attention to these issues, probing in great depth the gains Beijing can expect, the challenges it will face, and the new demands it will have to satisfy. Understanding those Chinese assessments is helpful as the United States considers how, when, and in what capacity to engage the BRI.