This paper is aimed at investigating the influence of political foundations on the domestic and foreign policies of state and analyzing the place and role of foundations in international relations. The relevance of this topic lies in the expanded use of semi-official and guerilla diplomacy instruments in the foreign policy toolkits of governments, which are widely financed by political foundations. The paper deals with the development of the contemporary political foundations of the United States and Germany, including a comparative analysis of performance features. We introduce a classification of the functions of foundations in the context of international relations. The conclusion is drawn that German political foundations are designed much like a ministry of foreign affairs with the elements of a political party, whereas the typical American philanthropic foundation is run much like a business corporation. German representatives tend to be present on the spot, continuously make contacts and keep track of local developments. Meanwhile, American foundations apply a project-based approach, and aim to create NGOs or partnerships geared towards concrete actions or tasks making claims for international legitimacy. Foundations in Germany and the United States are different in terms of funding models, degree of governmental involvement, scale and methods. Both serve as proxies and commentators of the ideology of the ruling elites, which contributes to the foreign policy aims of their countries of origin. By distancing themselves from official diplomacy and formal legal autonomy (although the programmes of the largest foundations are often consistent with the interests of their home country), foundations have plenty of room for manoeuvre and are thus able to penetrate the society of the target country and influence sensitive areas, such as education, domestic policies, the expert community, the media, etc. A great deal of ties and points of influence on social and power structures of a foreign country are thus shaped “from the inside,” and could be exploited to further the interests of the state of origin of a given foundations. The experience of Western foundations is actively employed by other, including non-Western, states and organizations. A range of tools could be applied to strengthen bilateral and multilateral cooperation within the framework of the Eurasian integration project of Russia according to the principles of mutuality and inclusivity.