Most visitors to Australia arrive by air. The main international airports are Sydney, Melbourne and Brisbane, followed by Perth, Adelaide, Hobart, Darwin and Cairns. There are plenty of connections from Asia, Europe and the USA, but Australia's remoteness makes flights expensive and long. Australia's current international popularity also means that many flights are heavily booked. Make plans well in advance!
Once there, Australia is so vast that up to 80% of long-distance trips within the country are also made by air.
There are several long distance bus companies. Buses are comfortable, but if you're travelling between major cities be prepared for a long trip.
Few people travel long-distances by train because it's usually the slowest mode of overland transport and remains relatively expensive.
An economical way of travelling round Australia would be to group together and hire or purchase a car.