Citizens from EU countries such as Iceland, Liechtenstein, Norway and Switzerland can enter and stay in Germany without a visa and don't need a work permit. They only need a valid passport.
Citizens from Australia, Canada, Israel, Japan, New Zealand, South Korea and the USA can enter Germany without a visa for up to 90 days. For a longer stay, however, they need to apply for a residence permit at the Immigration Office. If you are planning to start employment at HHU right after entry, it is advisable to already apply for a visa with work permit in your home country before traveling to Germany. Chosing to wait after entry can significantly delay the beginning of your contract due to waiting times at the Immigration Office. Note, that you cannot sign your contract at HHU without work permit in Germany.
Citizens of all other countries require a visa to enter Germany and need to apply for a visa at the German embassy in their country of residence.
For a short term stay (up to 3 months) you can apply for a Schengen visa (C-Visa), which allows you to travel freely within the Schengen states. When applying for the Schengen visa, please state "scientific work" or "research" as the purpose of your stay. Please note, that a Schengen visa cannot be extended and you are obliged to have left the Schengen area by the time your visa expires.
For a long term research stay (over 3 months) you need to apply for a National visa (D visa). Bear in mind, that it is not sufficient to first apply for a Schengen visa as you cannot change your visa status after having entered Germany. Please apply for one of the following visas:
- Study Visa (§16b Residence Act): for doctoral students without work contract
- Research Visa (§18d Residence Act): for doctoral students with work contract and all postdocs regardless of funding
To apply for a visa, you generally need an invitation letter from your supervisor or the university as well as proof of how you are going to finance your stay. Please enquire at the German Embassy in your home country about the respective requirements and regulations.
Find a general overview on visa requirements/waivers when entering Germany as well as the regulations concerning residence permits here.
For more information, check the website of the German Foreign Office.