by train: Euston, Kings Cross, St Pancras Stations

by tube: Warren Street, Euston (Northern, Victoria Lines)
Goodge Street (Northern Line)
Euston Square (Circle, Metropolitan, Hammersmith & City Lines)
Russell Square (Picadilly Line)

by air: from Heathrow Airport by tube to Russell Square (Picadilly Line),
or by train to Paddington (Heathrow Express), then tube to Euston Square (Circle, Metropolitan or Hammersmith & City Line).
from Gatwick Airport by train to Victoria (Gatwick Express), then tube to Warren Street (Victoria Line).
from Stanstead Airport by train to Liverpool Street (Stanstead Express), then tube to Euston Square (Circle, Metropolitan or Hammersmith & City Line).
from City Airport by bus to Canning Town (Green Shuttle Bus), then by tube to London Bridge (Jubilee Line), then by tube to Euston (Northern Line).