Bangkok is the main part of the good transport system in Thailand, with frequent domestic flights; operated mostly by Thai Airways and Bangkok Airways; trains and air-conditioned and ordinary buses linking Bangkok with all main cities around Thailand.

Buses:

Practically all cities and provinces are without difficulty reached by bus from Bangkok, buses are economical and air conditioned buses have major destinations marked in English. However, the schedules give the impression to change often; you can generally book a ticket at the last minute at the bus terminal but not always.

It is suggested you call the bus station with your intended destination to make sure you are going to the correct bus station and there are enough travel tickets. Though Bangkok is well linked to other cities, getting to the bus stations frequently are a challenge in themselves.

Bangkok features three official bus stations each one serving a different part of the kingdom:

The Southern Bus Terminal also known as Sai Tai Mai (+66 02 435 1200) on Phutthamonthon Sai 1, services buses arriving from west and the southern towns such as Hua Hin and Phuket.
The Northern Bus Terminal also known as Moh Chit 2 (+66 02 272 0296) on Kampaengphet 2 Road, is the largest, busiest and most modern, Buses leave frequently throughout the day, including to Ayuthaya, Kanchanaburi, Chiang Mai, near the Laos border and Lampang. Mo Chit sky train station, Kamphaeng Phet subway station and Chatuchak subway station are close to the station, the best way to reach the station is by taxi.
The Eastern Bus Terminal (+66 02 391 2504) also known as Ekamai located next to Ekamai BTS station on Sukhumvit Road opposite Soi 63. The terminal services buses arriving from the southeast coast, including from Pattaya, Rayong, Ko Samet, Chanthaburi, Koh Chang and other Eastern destinations.

Trains:

Thailand as it does at the geographical centre of the country has a very good railway system providing a cheap, safe, comfortable and friendly way for travel around the country. Travel by train is probably the best way to see extensively the country in a relaxed manner. Quite popular with tourists is a genuine Thai experience. The State Railways of Thailand is the official rail operator.

Taking a train is a great way to get you from Bangkok to, or close to, major destinations in Thailand including Chiang Mai (the travel takes around 14 hours on most overnight trains), Ubon Ratchathani, Surat Thani, Nong Khai, Koh Tao, Koh Samui, Koh Phanghan and other tropical islands of Thailand's coast. It is also a wonderful way to travel between Bangkok, Butterworth in Malaysia, Kuala Lumpur and Singapore.

The three main stations in Bangkok are:

Hua Lamphong Train Station (+66 02 223 3762) located on Rama IV Road, is the main station in Bangkok; built during the King Rama IV period. It is a good station, with many services, including baggage check, a small food court and a useful information counter. Payments by credit card are accepted.
Bang Sue Train Station hasn�t much information in English inside.
Thonburi Train Station also known as Bangkok is the starting point for services to Kanchanaburi, River Kwai Bridge and Nam Tok.

Crossing the border to Cambodia:

Most travelers from Thailand enter Cambodia the Aranyaprathet in Thailand and Poipet in Cambodia Border Crossing. The border crossing was opened in early 1998, the roads, although bad, are maintained to a reasonable quality. The border office is open from 07:30 to 17:00 hours; foreign tourists can get the visa here, you may be asked for a few sorts of vaccination certificate by the local immigration representatives.

Aranyapathet is over 200 kilometers from Bangkok to the West; the travel takes around 4-5 hours drive. Travelers can take a bus from the Northern Bus Terminal in Bangkok or take a train from Hua Lampong Railway Station of Bangkok. From the Train and Bus Terminal in Aranyapathet, the Poipet border is approximately 6 kilometers away.