Trains
The State Railway of Thailand runs from Bangkok in three main directions: north to Chiang Mai, northeast to Nong Khai and Ubon Ratchathani, and south through Surat Thani to the Malaysian border. Night trains with sleeper cars are a great way to cover long distances — comfortable, scenic, and cheap. Book a few days ahead, especially for sleepers, at any main station or through the SRT website.
Buses
Long-distance buses go virtually everywhere trains don't. Bangkok's main terminals are Mo Chit (north and northeast), Ekkamai (east), and Sai Tai Mai (south). VIP and first-class overnight coaches are reasonably comfortable and cost less than 1,500 THB even for long routes. The bus from Bangkok to Chiang Mai takes about 10 hours; to Krabi about 13.
Domestic Flights
Thailand has a well-developed domestic network. Thai Airways, Bangkok Airways, AirAsia, Nok Air, and Lion Air connect Bangkok to Chiang Mai, Phuket, Koh Samui, Hat Yai, and other destinations. Prices are competitive, especially if booked in advance. Flying is often the sensible choice for south-bound trips — a 12-hour bus ride versus a 90-minute flight at a modest premium.
Both Suvarnabhumi and Don Mueang airports serve as domestic hubs; check which one your flight uses, as they're 40km apart.
Ferries and Island Hops
Getting to the southern islands means a ferry or speedboat connection from the mainland. The main departure points are Chumphon and Surat Thani (for Koh Tao, Koh Phangan, Koh Samui), Krabi and Phuket (for Koh Lanta, Phi Phi), and Trat (for Koh Chang). Services run frequently in high season; in the wet season routes can be reduced or cancelled.
Around Town
In Bangkok, the BTS Skytrain and MRT metro are fast and cheap. Metered taxis are widely available — insist the driver use the meter, and add a small toll surcharge if using the expressways. Grab (the regional equivalent of Uber) works well in Bangkok and larger cities and avoids negotiation entirely.
Tuk-tuks are more of a tourist experience than a practical mode of transport in most cities — they're rarely cheaper than taxis and the drivers often steer you toward commission-paying shops. Songthaews (shared pickup trucks) are the standard local transport in smaller towns and on the islands.
Renting a Motorbike
Scooter rental is cheap and common on the islands and in Chiang Mai. Ride carefully: Thailand has high road accident rates, the roads can be rough, and many travelers' travel insurance specifically excludes motorbike accidents. Always wear a helmet, which is legally required and generally available with the rental.
Car hire is practical if you're exploring a specific region like the north, but driving in Bangkok makes little sense given the traffic and limited parking.