Public transportation from Helsinki Vantaa Airport:

The new 18 km Ring Rail Line train connection, partially underground, with direct entrance to the Airport terminal opened late December 2015 upon completion of the elevators.  Escalator installation at the entrance will continue into early 2016 - until then, the shuttle bus continues to run between the Tietotie entrance & the terminals. 
Thereafter, passengers may travel directly from the Airport to Helsinki's city center by train.  (Both Helsinki Airport & Aviapolis stations are 40 meters below ground.)  Passengers may board the train directly at the new train station under the Terminal, accessible from  its sub-level, reached via escalator or elevator.
Those catching long-distance trains (which use the Ring Rail Line) may change over at Tikkurila station which
offers connecting  commuter & long-distance trains (including to St.Peterburg & Moscow).
Ticket Purchase:  You can buy a ticket from the ticket machines on the platform (at the further end of the station, where entrance to the terminal will be opened there later.  The regional ticket costs around 5 euros. valid 90 minutes from the time of purchase on all HSL transport within Helsinki, Vantaa, Espoo & Kaunianien.

As of Nov. 16, 2015, a new Commuter Bus Route 617 from/to Hameentie & Maekelankatu will run every 30 minutes at rush hours and run along Tuusulanvayla & Ring Road II, and also serves areas next to Ring Road III & Lentoasemantie. 

Daytime & overnight buses by Matkahuolto & ExpressBus depart from the Airport Coach Terminal. 

Bus stops at T1
Bus stop 1: Finnair City Bus
Bus stop 3: to Tampere

Bus Stops at T2
Bus across from Arrivals 2A:
Bus stop 10: Finnair City Bus
Bus stop 13: to Tampere
   (b) Buses across from Arrivals 2B include Bus Stops 11-14, 21-24, 31-34 & a bit further southwest of Bus 34 are buses 35, 36:
Bus stop 3 is to Tampere
Bus stop 11: AirPort Bus, hotel shuttle buses
Bus stop 12: Bus to Remote Car Park Bus stops 13–14: Express buses, bus 540
Bus stop 21: Bus 615 to Helsinki city centre, 620N
Bus stop 23: Buses 519, 519A, 520
Bus stop 24: Bus 51

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