»›Extremism Clauses‹ in Parliamentary Law«: The standardization of an »extremism clause« is considered a means of protecting the free democratic basic order as well as the functionality and integrity of the German Bundestag and the federal state parliaments. This paper examines whether such a clause can make a meaningful contribution to ensuring institutional resilience against anti-constitutional tendencies, what requirements such a clause must meet and how effective and legally secure enforcement could be designed.