Transnational activism has become increasingly salient dynamics of world politics in recent decades. Thousands of transnational actors -advocacy networks, social movements, non-governmental organizations and other activists- work for various causes regarding human rights, environment, women’s rights, development, peace and etc. Overall, transnational activism challenges the fundamental characteristic of the modern nation-state system: sovereignty. As a result, the increasing quantity of transnational activism has led to controversies in the field of international relations (IR) theories. While realist theories look them skeptically, neoliberal institutionalism gives them some role in world politics. Constructivism takes them seriously as carries of norms and challengers of state sovereignty. It also greets them being source of change in world politics. The paper examines IR theories in regard to transnational actors.