The efficiency and effectiveness of the international non-governmental organisations (INGOs) in ensuring peace and security as relevant and growing only in dynamic interaction and cooperation with other international actors (international governmental organisations, non-governmental actors, and civil society institutions) have been justified. The features, models and problems of interaction of INGOs with other international actors in maintaining peace, stability and security, solving and preventing modern security challenges of the international system have been comprehensively studied. Such interaction and coordination of the efforts of INGOs and other international actors is viewed through the prism of expanding the areas of competence of non-governmental international organisations and increasing their activity in various areas. Some examples of an active involvement of non-governmental organisations in the activities of the UN (and its structures), NATO, OSCE, CoE, EU are given. Challenges of the interaction of governmental and non-governmental sectors in the international arena are analysed. International non-governmental actors, being independent (mostly) of their governments and officials of other international structures, are emphasised to have the opportunity to respond to strategic security challenges quickly and effectively, update public opinion, and mobilise the international community to address security issues at the regional and global levels.