Nationals from an EU member state (or from an EEA country or Switzerland)

Labour mobility and freedom of trade apply within the EU member states as well as the EEA countries and Switzerland. EU citizens who wish to move to a member country do not require a residence permit and may set up a business in any of the member states. However, there are some exceptions. More detailed information regarding this can be found on the website of the Federal Office for Migration and Refugees.

Nationals from a non-EU country

Nationals from a non-EU country wishing to enter Germany in order to engage in a self-employed activity are required to apply to the respective foreign mission of the Federal Republic of Germany for a residence permit for the purpose of self-employed commercial activity.
Under certain circumstances, foreigners who are already resident in Germany and who have received a residence permit for a purpose other than self-employment can engage in self-employed activity. More information about this can be found on the website of the Federal Office for Migration and Refugees.

IQ Fachstelle Migrantenökonomie has also published a guide for people from non-EU countries starting a company.