Think tanks are nonprofit policy research organizations that produce and promote analysis and expertise in order to be influential with policymakers. Beginning in the 1970s, their number exploded in the United States. The proliferation of think tanks represented a hope that lawmaking, in fact, might become better informed and more reasoned as a result of their expert contributions. Instead, as this book documents, the known ideologies of many, especially newer, think tanks contributes to an environment in which they are often little different from advocacy organizations, promoting points of view and preordained policy prescriptions. As a result, these organizations fail to achieve the substantive influence that they might, and their behavior has helped undermine the credibility with which experts and expertise are generally viewed by policymakers.