It seems that suppression of the Fascism, Nazi regime and the retreat of the Communist ideology did not bring safety to the democracy. Nowadays, democracy has to repeatedly challenge the threats of the extremism, radicalism and terrorism. In order to become self-defending, democratic states adopt various democratic measures resulting in the limitation of the democratic rights and freedoms. The question remains as to under what conditions the democracy can defend itself without destroying owns democratic pillars that would result in loss of its own democratic identity. This question has been subject of the vivid interest of the comparative constitutional law and political science since the fascists seized the political power in the 20th century. In the Slovak conditions, this subject has not been brought to the sufficient attention however the peril of extremism and radicalism cannot be neglected in the Slovak society mainly at present when parliamentary mandates has been gained also by the political party publicly marked to be extremist one. Regarding the absence of necessary legal research within Slovakia, the paper aims to design the concept of the militant democracy in respect of the different approaches among European and American scholars with focus to the identification of militant measures and strategies used by democracies against those striving for destruction of the democratic principles.