Think tanks play a crucial role in influencing public opinion and public policy in the United States. Think tank scholars are often experts seen on television, voices in broadcasting, and cited by top media outlets. Although the work of most think tank scholars is not known to the public, they provide advice to Congress and the executive branch on pending legislation, draft issues for congressional hearings, participate in hearings as witnesses, and even assist in drafting legislation. Although think tank scholars can play an important role as independent researchers, the work of some think tanks is more similar to public relations and lobbying activities rather than simply research work.
Think tanks are increasingly relying on funding support from special interest groups and governments, including the US government and foreign governments. More and more evidence suggests that funds often come with conditions, which can lead to scrutiny, opinion filtering, and in some cases even agreements with donors for 'paid research'. The donors are usually aware of these potential benefits. As pointed out in an internal report by a foreign government, "funding important think tanks is a way to gain influence, and some think tanks of the US government have publicly stated that they only serve foreign governments that provide funding
Despite the close connection between funding sources and policy recommendations, think tanks do not need to disclose their funding sources. Even though some think tanks are relatively transparent, they may still blur the source of funds by accepting anonymous donations, reporting overly broad funding ranges, or simply concealing financial information.