International flights
The capital Ulaanbaatar (UB) is the only city that has international airport for now.
if you are coming from west then you can take the route: a. Frankfurt direct flight to Ulaanbaatar, b. Istanbul to Ulaanbaatar via Turkish airlines
USA-istanbul-Ulaanbaatar
if you are coming from south east asia:
USA-Korea/Japan-Ulaanbaatar via Korean air and MIAT or USA-Beijing-Ulaanbaatar via AirChina and MIAT
Hong Kong/Thailand-Beijing/Seoul- Ulaanbaatar via MIAT or Airchina