Before travelling to Germany, one of your first steps will be to consider whether you will need a visa. All necessary information about this topic is provided by the German Federal Foreign Office.
The IO would like to draw your attention to an important point to consider:
Although holders of passports from countries marked “no” on the list provided do not require a visa to enter Germany, this does not mean that they can take up gainful employment (unless otherwise stated).
If you are from the above-mentioned countries and plan on working at AEI for more than 90 days with an employment contract, it is recommended to apply for a national visa (D). This visa is a temporary entry visa (valid for 90 days) which will allow you to travel to Germany. It usually also notes your intended work activity in the remarks section.
In order to work and stay in Germany for more than 90 days, you will then have to apply for a residence permit once you arrive in Germany at the local Foreigners' Office.
If you do not apply for an entry visa, you will not be able to lawfully work until you apply for, and receive, a residence permit. This will require a considerable amount of time, as there are also a few other formalities to take care of beforehand.
Scholarship/fellowship holders are unaffected by this regulation as they are not employees.