VERY IMPORTANT: FOR ALL NON-EU STUDENTS HOLDING A GERMAN VISA OR A GERMAN RESIDENCE PERMIT UNDER §16B. PLEASE BE AWARE THAT YOUR LONG TERM VISA OR RESIDENCE PERMIT LOSES VALIDITY ONCE YOU HAVE LEFT GERMANY FOR MORE THAN SIX MONTHS. PLEASE CHECK AND RE-CHECK YOUR CERTIFICATE OF ENROLLMENT.
If you are a citizen of a Schengen state you won't need neither a visa nor a residence permit to enter Germany.
For your reference, these are all the 29 Schengen states: Austria, Belgium, Bulgaria, Croatia, the Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Italy, Latvia, Liechtenstein, Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden and Switzerland.