By plane
Christchurch in the South Island's biggest international airport with flights from all around the Pacific Rim. Dunedin and Queenstown both have flights from Australia.
There are many airports which have scheduled flights into the South Island, including Picton, Blenheim, Nelson, Takaka, Westport, Kaikoura, Greymouth, Christchurch, Timaru, Dunedin and Queenstown.
Invercargill airport has flights to Stewart Island. Christchurch airport has flights to the Chatham Islands.
By ship
The Interislander (http://www.interislander.co.nz) and the Bluebridge (http://www.bluebridge.co.nz) ferry companies run from Wellington to Picton through the Marlborough Sounds and across Cook Strait. The ferries take cars, buses and trains. The scenery on a good day is spectacular. The ferries are substantial ships designed for the sometimes rough conditions and the journey takes between 3 and 3 1/2 hours.