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 this Embassy beforehand in order to get further information about the needs and requirements for the Visa. Please note furthermore when applying for a Visa, the reason for your journey should be research purposes. Among other documents, an invitation letter from the MPI might be needed. You will receive such an invitation letter from the Max Planck Institute for Dynamics of Complex Technical Systems for your visa application. This is generally issued by the MPI department with which you are in working contact. 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 for more than three months. Tourist Visas cannot 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 Affairs Office.