The conventional wisdom of US foreign policy has at its core a set of widely held yet underexamined beliefs. Together, these notions constitute the essence of what has become tendentiously known as “the blob,” or the official mind of US national security. Debates and analyses can proceed more productively if foreign policy beliefs, rather than the people who hold them, are moved to the center of analysis. The blob is a mindset, not a group of individuals—one that is based on a few basic assumptions about the world and the United States’ place in it. This article describes what those beliefs are and how they influence US foreign policy.