Most of the over 500 million residents in the European Union (EU) are permitted to enter the Rhine Ruhr region of Germany. Freedom of movement regulations within the EU normally makes that possible without possessing a visa or even showing a passport.
However, everyone who wishes to remain and work in a country other than that of their own nationality must register with the authorities if their stay is to exceed ninety days. The local registration office (Einwohnermeldeamt) will then issue a residence permit.
For others, it is not quite so simple. Most other foreigners from outside the European Union member countries need a visa but may under certain circumstances be able to move freely. Those entrepreneurs staying under ninety days per six month period to work who wish to set up a business, should apply for a Schengen Visa.
Non EU nationals wishing to run a business or take up employment in Germany need to apply for a national German visa to enter the country. This is intended for stays of ninety days or more. Generally speaking, there are many exceptions and specific regulations depending on the nationality of the person applying.
Residency and settlement permits such as the blue card are also complex topics, again depending upon nationality.