By plane:

two international airports
(direct flight connection to 250 cities):
Chopin Airport (10 km from the City Center) and Modlin Airport (35 km from the City Center)
By car:

from Berlin (via A2 highway), Dresden (A4+A1), Prague (A1) or Lviv (A2+A1). Please mind the speed limits :)
By train:

Three stations with direct connections to Berlin, Bratislava, Prague, Vienna, Budapest and Kiev!
By bus:

International bus terminal with direct connections to various European cities including London, Paris, Berlin, etc…