By plane
Tasmania is served by several national and regional airlines, primarily flying into Hobart and Launceston. Some flights are also available to Burnie, Devonport, King Island and Flinders Island from Melbourne.
By ship
Tasmania is served by two Spirit of Tasmania Ferries (http://www.spiritoftasman...) from mainland Australia. They depart daily from Station Pier in Port Melbourne a bayside suburb of Melbourne and arrive at Devonport taking the full night or the full day during peak summer periods for the crossing.
The crossing can be a little rocky at times, but provides beautiful views. You have the option of booking one of a range of a cabins or a reclining chair for the journey. The large ferries take vehicles, bikes, foot passengers and pets.
See the Devonport article for the details of the ferry.
Rental car companies usually have restrictions on taking vehicles into or out of Tasmania on the ferry. If you have hired a car on the mainland and need a car to hire in Tasmania, it's best to drop the car off in Melbourne CBD there is no hire car dropoff at Station Pier, then take the 109 tram out to Station Pier the terminus is across the road from the ferry terminal; car hire is available at the Devonport terminal.