I've flown through Frankfurt over a dozen times connecting to destinations in Europe, Asia and Africa. If your flight is a Transit connection, then you will just go to your next gate and you don't have to go through immigration. Typically, you go through immigration when your connecting flight is domestic and/or you leave the international terminal. Many international airlines will wait for connecting Transit passengers (if it's within a reasonable amount of time). When you disembark your flight, you will see signs for "Transit" and "Immigration / Passport Control" After you depart your flight, remember to ask the gate attendant for the gate number of your connecting flight and follow the signs for "Transit." The gates in the international terminal are not always staffed. If you accidently go through immigration / passport control, then you will have to go through security again and maybe even have to check-in at the ticket counter. The gates in the international terminal are not always staffed. I hope this helps.