The term "think tank" was introduced in the United States during World War II to characterize the secure environment in which military and civilian experts were situated so that they could develop invasion plans and other military strategies. Some observers believe that think tanks fall in the gray areas of the civil society concept since they are organized to, at least indirectly, advise and/or assist government. One role performed by many think tanks, especially those with staffs composed primarily of Ph.D.s in the social sciences, is carrying out basic research on policy problems and policy solutions in a fashion similar to that done by university-based researchers. A second role performed at many think tanks is providing advice on immediate policy concerns that are being considered by government officials. The chapter also presents an overview of the key concepts discussed in this book.