Picture choosen by: Mr.Davindar Singh Getting into Thailand Visa-on-arrival is available at certain entry points for passport holders of 20 other nations, including India and China. Check the latest scoop from the Ministry of Foreign Affairs. By law, you must carry your passport with you at all times.

By plane
Bangkok is one of Asia's largest hubs as well as the busiest airport in Southeast Asia; practically every airline that flies to Asia also flies to Bangkok, meaning competition is stiff and prices are low.
There are also international flights directly to/from Chiang Mai, Ko Samui, Phuket, Krabi, Hat Yai and Udon Thani.
The national carrier is the well-regarded THAI Airways, with Bangkok Airways filling in some gaps in the nearby region. Bangkok Airways offers free internet access while you wait for boarding to start at your gate.
Chartered flights from and to Thailand from international destinations are operated by Hi Flying group. They fly to Bangkok, Phuket, Koh Samui and Udon Thani.

By road
Cambodia - six international border crossings. The highway from Siem Reap and the temples of Angkor via Poipet to Aranyaprathet, once the stuff of nightmares, is now merely bad and can usually be covered in less than 3 hours.
Laos - the busiest border crossing is at the Friendship Bridge across the Mekong between Nong Khai and the Lao capital Vientiane. It's also possible to cross the Mekong at Chiang Khong / Huay Xai, Nakhon Phanom / Tha Khaek, Mukdahan / Savannakhet, and elsewhere.
Vientiane / Udon Thani - A bus service runs from the Morning Market bus station in Vientiane to the bus station in Udon Thani. The cost is 80 Baht or 22,000 Kip and the journey takes two hours. The Udon Thani airport is 30 minutes by Tuk Tuk from the bus station and is served by Thai Airways, Nok Air and Air Asia.
Malaysia and Singapore - driving up is entirely possible, although not with a rented vehicle. Main crossings (with name of town on Malaysian side in brackets) between Thailand and Malaysia are Padang Besar (Padang Besar) and Sadao (Bukit Kayu Hitam) in Songkhla province, Betong (Pengkalan Hulu) in Yala province, and Sungai Kolok (Rantau Panjang) in Narathiwat province. There are regular buses from Singapore to the southern hub of Hat Yai.
Myanmar:
Mae Sai / Tachileik - foreigners can access this crossing from either side, and enter and/or exit either country here; no onward travel restrictions; to get to Tachileik or Kengtung from the rest of Myanmar, a domestic flight must be taken (eg from Heho).
Mae Sot / Myawaddy - foreigners can only access this crossing from the Thai side; neither onward travel into Myanmar (ie beyond the border town) nor overnight stays are possible. No visa needed; instead there's an entry stamp fee - USD10 if paid with USD notes, more (500 baht) if paid with Thai currency.
Three Pagodas Pass (Sangkhlaburi / Payathonzu) - foreigners can only access this crossing from the Thai side; onward travel into Myanmar (ie beyond the border town) is not possible; entry/exit stamps are NOT issued here, and foreigners passports are held at the Myanmar checkpoint, where a fee is levied - USD10 if paid with USD notes, more (500 baht) if paid with Thai currency. However, as of November 25, 2008, this crossing is temporarily closed.
Ranong / Kawthoung - foreigners can access this crossing from either side, and enter and/or exit either country here; no onward travel restrictions (other than those that apply to everyone, no matter how they enter); access to/from Kawthoung is by sea (Mergui/Dawei & Yangon) and air (Mergui & Yangon). If entering without a visa, maximum stay is 3 days / 2 nights, travel beyond Kawthoung is not permitted, and there's an entry stamp fee - USD10 if paid with USD notes, more (500 baht) if paid with Thai currency.

By train
Thailand's sole international train service links to Butterworth (near Penang) and Kuala Lumpur in Malaysia, continuing all the way to Singapore. Tickets are cheap even in first class sleepers, but it can be a slow ride; the 2-hour flight to Singapore will take you close to 48 hours by rail, as you have to change trains twice. The luxury option is to take the Eastern & Oriental Express, a refurbished super-luxury train that runs along the same route once per week, with gourmet dining, personal butler service and every other colonial perk you can think of. However, at around US$1000 one-way just from Bangkok to Butterworth, this is approximately 30 times more expensive than an ordinary first-class sleeper!
While you can't get to Laos or Cambodia by train, you can get very close, with railheads just across the border at Nong Khai (across the river from Vientiane) and Aranyaprathet (for Poipet, on the road to Siem Reap). A link across to Mekong to Laos is open in March 2009, but service to Cambodia remains on the drawing board.
There are no rail services to Myanmar, but the Thai part of the infamous Burma Death Railway is still operating near Kanchanaburi.

By ferry
It is possible now to travel by ferries in hi season(Nov-May) from Phuket and island hop your way down the cost all the way to Indonesia.
This can now be done without ever touching the mainland, Phuket (Thailand) to Padang (Indonesia).
Islands on rout:
Ko Phi Phi
Ko Lanta
Ko Ngai
Ko Mook
Ko Bulon
ko Lipe-Koh lipe being the hub on the boarder between Thailand and Malaysia having a Thai immigration office.
Langkwai- Malaysian immigration here.
Penang
Note:Thai portion can be done in a day.
Ferries cross from Satun in southern Thailand to the Malaysian island of Langkawi, while over in Narathiwat province, a vehicular ferry shuttles between Tak Bai and Pengkalan Kubur, near Kota Bharu in Malaysia's Kelantan state.
There are also occasional cruises from Malaysia and Singapore to Phuket and Bangkok, the main operator being Star Cruises, but no scheduled services.