Sardinia is compact enough that you can cover a lot of ground in a week, but public transport is patchy outside the main cities. If you want to explore the interior or reach remote beaches, a hire car is effectively essential.
Car
Renting a car is by far the most practical way to get around. Roads are generally in good condition and reasonably well signed. Traffic is light except on the coastal roads in August, when the island is heaving. Petrol stations can be scarce in the mountainous interior, so fill up when you can. Most rental companies have desks at all three airports.
Bus
ARST operates an island-wide bus network that connects most towns and villages. It is slow but cheap. Several bus routes only run once or twice a day, and some services are reduced or suspended outside summer. Macomer, roughly in the centre of the island, is a major interchange where many routes meet.
Train
The state rail network (Trenitalia) connects Cagliari to Oristano, Sassari, and Olbia, though the journey times are long. A separate narrow-gauge network, the Trenino Verde ("little green train"), runs scenic routes through the interior — it's more of a tourist experience than a practical way to travel, but the views are memorable.
Ferries
Local ferries connect the mainland ports of Olbia and Palau to the islands of the La Maddalena Archipelago. A regular service also runs between Portovesme (near Carbonia) and Carloforte on the Isola di San Pietro.