This dissertation addresses the question how democracies defend themselves from political parties and groups which profess antidemocratic values and use violence as one of the means to achieve their goals. In particular this dissertation analyses the range of formal-legal measures and provisions that democracies have at their disposal to constrain their non-democratic groups and political parties, looking at eight advanced European democracies Austria, Belgium, Denmark, France, Germany, the Netherlands, Sweden, and the United Kingdom. These measures and provisions are identified in constitutional documents, civil law, criminal law, in electoral laws, and other pertinent legal sources passed by the legislature and issued by courts of these countries, pertaining to the regulation of political freedoms, public order, and homeland security. On this basis, the thesis provides an encompassing and systematic assessment of differences and similarities between these democracies and thereby assesses their relative formal-legal democratic defensiveness.