A lot depends on circumstances, I know a guy that tours all the time and when he goes to a different country he gets for free a cheap bike box from a LBS then discards it once he picks it up in the other country, then just finds another LBS there to get a box for the return trip. If you box it, cover all the frame and fork with foam pipe insulation it's cheap and works. He covers the entire frame by cutting to fit the tubes, covers the forks, covers the handle bars; wraps all loose parts like seat, the handlebars again, pedals, crank which he also ties to the chainstay, etc with bubble wrap. Places a piece of wood about 2" inches round between the fork blades at the dropouts to prevent the forks from getting bent. covers the wheels with bubble wrap and deflates the tires to about 20psi by air, seals the box with wide strapping tape and off he flies. Uses his panniers as suitcases on the plane, puts the pannier frames in a different box sometimes with a bag.
There are sites that can show you how just search.
But he has a Rivendell, and he has shipped his bike like this 5 times to other countries with no problems other then the escalating cost of doing it over the past few years.