If you are expecting a visitor from a country requiring a visa for Germany, this usually requires a letter of invitation. The visitor should go to the German Embassy with this invitation and apply for a visa. The invitation letter should contain at least the following information:

• Subject: Request for a national visa
• Name and date of birth of the guest
• Reason / purpose of stay at the TU Berlin
• Period of stay
• Name of the faculty / institute / department and the supervisor
• Financing of the stay (scholarship, employment, self-paid)

The addresses of the German embassies and consulates can be found here.