For short-term stays in Germany (up to 90 days in any 180-day period) all non-EU citizens require a Schengen visa to enter Germany. With this visa, entrepreneurs can perform most activities necessary to set up their business in Germany. For more information, please refer to the following site:
Is the duration of the stay exceeding 90 days (in any 180-day period) or is a (self-employed or gainful) occupation taken up, a national visa is required to enter Germany. In Germany, this national visa must be converted into a residence or settlement permit by the responsible local immigration office (Ausländerbehörde) in order to stay in Germany according to the intended purpose of the trip.
However, there are visa exemptions for several countries. Citizens from Argentina, Australia, Brazil, Canada, Hong Kong, Israel, Japan, Mexico, New Zealand, South Korea, the United States and some other countries may stay in Germany up to 90 days without any visa. Still, a national visa is required when entering Germany for long-term stay purposes or when a (self-employed or gainful) occupation is taken up.
Only citizens from Australia, Canada, Israel, Japan, New Zealand, South Korea, and the United States may enter Germany for long-term stay purposes without a national visa (exception: ICT card). These foreign nationals may directly apply for the necessary residence or settlement permit at the immigration office (Ausländerbehörde) in Germany.
The Federal Foreign Office (Auswärtiges Amt) is able to provide detailed information on individual rules for certain countries.