The Copenhagen School approach to security studies is a critical approach that also draws on ideas of constructivism. It is an approach that is unique largely in its focus on the way in which issues of security interact with domestic politics.
The Copenhagen School emphasizes the idea of “securitization.” This term is used to refer to a process by which certain actors take issues of domestic politics and transform them into issues of national security. When they do this, they give themselves much more freedom of action because the issues come to be seen as issues of national security which are, therefore, above politics.
The Copenhagen School is connected to constructivism because it focuses on how threats to national security are socially constructed. It argues that political actors work to portray certain issues as threats to national security. For example, in the US, the war on terror can be seen in this way. Because political actors have (this school would say) convinced us that terrorism is a serious threat, we have allowed them to take extraordinary actions so long as they say that these actions are being taken to prevent terrorism. We can see this in the reaction to the revelations about programs in which the government has been collecting data about phone calls that we make. Ordinarily, this would make most Americans very angry. However, the government has defined this as something that has to be done to protect us from terrorism. Therefore, it becomes a matter of security, not of personal rights and liberties.
This is what is unique about the Copenhagen School. It focuses on how the idea of security is invoked and used by political actors to give themselves more freedom of action on issues than they would have if they did not “securitize” those issues.