Substantial aspects of the right to demonstrate are guaranteed by the basic rights of assembly and freedom of expression, which stand in a complex mutual relationship to the requirement of democracy in the german basic law. Because of their contents demonstrations often are a challenge for the - dissenting - majority of the citizens and politicians. Hereby but even more because of casually occurring acts of violence they become a problem of police law. The habilitation thesis builds a bridge from fundamental questions of basic rights and administrative law to practical application; it includes the law concerning processions and assemblies and those legal regulations of criminal law which are important for demonstrations. The study considers aspects of constitutional history and of legal comparison (USA, Europe) as well as jurisdiction (Federal Constitutional Court, Administrative Courts). The results are translated into a pattern draft of a law concerning assemblies.