in many other European countries, in Germany allowed to have dual citizenship. If a citizen of Germany wanted to get the citizenship of another state, you will have to abandon the German. However, in almost every rule there are exceptions. And it is the same with German law.
If, for example, the citizen of Germany just concluded a marriage with a citizen of another country or, for instance, has invested a large sum in the business of Montenegro, the citizenship is automatic, and it is believed that man is not made active efforts to this and not put obtaining a second passport is the main goal. In this case, to have dual citizenship, legally. The state is also allowed its citizens to have a temporary immigration status in other countries (residence permit and permanent residence).