In many cases, especially for citizens from countries outside the EU, a visa is needed to enter Germany. You can apply for it at the German Embassy in your own country. Please contact the appropriate embassy beforehand in order to get further information about the requirements for the visa. Note when applying for a visa, the reason for your journey is research purposes. Among other documents, an invitation letter from the MPI might be needed. The Welcom Office, the administration or the secretaries will be happy to provide you with such a letter - just contact one of us. Remember also that a valid passport is needed for getting the visa and for entering Germany.
Generally, a visa is issued for the short term of 90 days. If you intend to work and stay for a longer time, you need to apply for a residence permit at the local foreigners' office shortly after your arrival.
Do not enter Germany with a tourist visa if you want to work or study here. Tourist visas can not be changed into a residence permit!
Citizens from EU countries will only need a valid passport.
More information on the entry of residence in Germany can be found on the webpage of the German Foreign Aiffairs Office: http://www.auswaertiges-amt.de/sid_B2BD6A10B3A782CE497B4220837EE1FA/EN/Startseite_node.html