The country is small — Santo Domingo to Puerto Plata is about four hours — and the roads are mostly decent, so most people cover it by bus or hired car.
Long-distance buses are good. Caribe Tours and Metro run modern coaches between the capital and the main cities on fixed schedules, air-conditioned to the point of cold, and they cost very little. Book the Samaná and Puerto Plata runs a day ahead in high season.
Guaguas are the local alternative: minibuses that leave when full, stop anywhere, and go everywhere the coaches don't. They are cheap, slow and crowded, and they are how the country actually moves.
Driving is straightforward on the main highways — the Autovía del Este to Punta Cana and the Autopista Duarte north are both fast toll roads — and demanding everywhere else. Expect motorbikes on the wrong side, livestock, unlit vehicles after dark, and the occasional unmarked hole. Driving at night outside the cities is best avoided. A car makes the south-west and the mountains far easier, and adds little in Punta Cana, where the resorts run shuttles.
Motoconchos, the motorbike taxis, are ubiquitous, cheap and by some distance the most dangerous way to travel here. Helmets are rarely offered.
Domestic flights link Santo Domingo, Punta Cana, Puerto Plata, Samaná and La Romana, and are worth it only for Samaná or if you are short on days.