Think tanks undertake research, analysis, and engagement that generate policy advice on domestic and international issues, enabling policymakers to make informed decisions and bridging the gap between the government and the public. In 1993 at the first global meeting of groups in Barcelona, Spain, many scholars believed that the term "think tank" did not travel well across borders. The chapter discusses their dramatic growth over the last quarter-century, and their increasing influence in global governance, and details progress and problems of think tanks. Think tanks can use their knowledge to assist policymakers and other actors who are immersed in the daily affairs of governing and have less time for analysis. The best and most powerful opportunity for think tanks and policy networks to affect or influence global policy is their ability to provide policymakers with important field research and up-to-the-minute information on critical issues or on geographically and socioeconomically disparate populations.