ICN Public Transportation Incheon Airport

Public transportation from Incheon Airport to your destination is available by bus, subway, train or Ferry:  For information about limos, premium buses and ticketing, visit one of these booths: Exits 4 &9 (indoors) or exit 4, 6, 7, 8, 9C,11, & 13 (outdoors). 
A new 'terminal' for mini van taxis or 'call van' service enables passengers now to be protected from fraud by enforcing fixed pricing, and vans can more easily load luggage there. 
An information desk located in the terminal between exits 12 & 13 of level 1 provides more information & fares.
The T-money Mpass card can be used for transportation anywhere in Korea - available at the Arrivals level East & West.
To transfer to Gimpo Airport, use the AREX train station:

By Train: 
The Airport Station is located on level B1 of the Transportation Center, where you can catch the Express Train to Seoul Station - or you can take the various commuter trains (there is a 24-hr service to Digital Media City).  Note that the link between Incheon Airport railroad & Gyeongui Line has been completed, and a Honan Line has been added.
  - Subway:  Lines 1 or 4 run to Seoul Station. Commuter trains connect you to the following lines & subway stations (only Gyeyang is an Incheon Subway, all others are Seoul subways):  Gyeyang - line 1; Gimpo Airport - lines 5, 9, Digital Media City - Line 6; Hongik University - line 2; Gongdeok - lines 5, 6.
  - AREX train station is in the Transportation Center, next to the main terminal. Both Incheon & Gimpo airports are express & commuter stations.  Commuter train stations are: Incheon Cargo Terminal, Unseo, Geomam, Gyeyang  (27 mins, with transfer to Incheon Subway Line 1); Gimpo Airport (33 minutes, with transfer to Seoul Subway Lines 5 & Digital Media City Station (transfer to Line 6, Gyeongui Line); Hongik University, Gongdeok; and Seoul Station (5 mins.; transfers to lines 1&4 & Gyeongui Line 9).
The AREX train station is equipped with a city air terminal & baggage processing facility, enabling passengers to check in there.
 - the Geomam station offers connection to the A'REX Airport rail link and high-speed main line services,
 - the Juan station offers connection to the Seoul metro Line 1,
 - the Incheon City Hall station offers connection to the Metro Line 1.
 - Metro Line 2 connects the north area of the city (Seo-gu) with the rest of the city and ending its route at the South-East (Namdong-gu). Line 2 with 27 stations (5 above-ground) is served by 37 driverless two-car train sets is 34·4 m which can hold 206 passengers.
 - [ By 2020, the Seongnam station will offer connection to the Seoul Metro Line 7. ]
  - Maglev Train Circle (max. speed 110 km/hr):  Its first phase of construction linked Incheon Airport with the Yongyoo-Mui leisure complex, a 6.1 km track covering six stations - taking 15 minutes. Phase 2 of construction thereafter will add another 9.7 km to the north-west of the island, while Phase 3 concludes the circle line by adding another 37.4 km.
 - KTR (Korea Train Express) offers a link between Incheon Airport Railroad, Gyeongui  & Honan.

By Bus: 
Nighttime bus service between the Airport & downtown Seoul increased to eight round trips - 4 round trips by Seoul Station line, and 4 by Gangnam Express Bus Terminal line (an 80-minute trip).  Buses heading for both Seoul Station & Gangam Terminal stop at Songjeong & Yeomchang Stations.
  Bus destination and bus stop locations: 
- Jamsil subway station - 11A
- local buses - 9C, 10C
- to Bus station - 1-14
- to Seoul - 3B-6B, 10A-13A;
- to Incheon - 2A, 2B, & 13B
- to Gyeonggi  - 7A,9B;
- to other provinces 1-14, 9C, 9D, 10C;
- shuttle busses stop at 3A, 13B; 
- bus charters stop at 1C, 12C.

By Ferry: A ferry service on Yengjong pier runs between the Airport and the city of Incheon, however its dock is quite far from the airport & you will need separate transportation to get there.