Dalaman Airport is the closest, ninety minutes by car east of Marmaris, with summer flights from across Europe and direct connections to Istanbul. Bodrum Airport to the west is about two and a half hours. Both have airport shuttle buses (Havaş) to Marmaris timed to flights, and taxis for around €50 from Dalaman.
By land, frequent intercity buses run from Istanbul, Ankara, and Izmir to the Marmaris otogar (bus station) on the inland side of town. Local dolmuş minibuses connect from there to the seafront and to neighbouring villages.
By sea, daily ferries run in summer from Marmaris to Rhodes — a 50-minute hydrofoil ride to the Greek island just across the strait. The ferries leave from the small port at the western end of the marina; bring your passport and budget for the visa formalities at the Greek end.