The number and frequency of festivals and fairs in Thailand is incredible - there always seems to be something going on, especially during the cool season between November and February. The exact dates for festivals may vary from year to year, either because of the lunar calendar, which isn't quite in sync with the solar calendar - or because local authorities have decided to change festival dates.

January
That Phanom Festival - An annual week-long homage to the North-East's most sacred Buddhist stupa (Phra That Phanom) in Nakhon Phanom Province. Pilgrims from all over the country, as well as from Laos, attend.

February
Chiang Mai Flower Festival - Colorful floats and parades exhibit Chiang Mai's cultivated flora.
Magha Puja (maakhá buuchaa) - Held on the full moon of the third lunar month to commemorate Buddha preaching to 1250 enlightened monks who came to hear him 'without prior summons'. A public holiday throughout the country, it culminates with a candle-lit walk around the main chapel (wian tian) at every wát.

Late February-Early March
Chinese New Year - Called trùt jiin in Thai, Chinese populations all over Thailand celebrate their lunar New Year with a week of house-cleaning, lion dances and fireworks. The most impressive festivities take place in the Chinese-dominate province capital of Nakhon Sawan.

March
Phanom Rung Festival - A newly established festival to commemorate restoration work in the Phanom Rung Historical Park, an impressive Angkor-style temple complex in Buriram Province. It involves a daytime procession up Phanom Rung Hill and spectacular sound-and-light shows at night. It takes place on the last week of the month.

April
Songkran - This is the celebration of the lunar New Year in Thailand. Buddha images are 'bathed', monks and elders receive the respect of younger Thais by the sprinkling of water over their hands, and a lot of water is generously tossed about for fun. Songkran generally give everyone a chance to release their frustration and literally cool off during the peak of the hot season. Hide out in your room or expect to be soaked; the latter is a lot more fun.

May
Visakha Puja (wísăakhà buuchaa) - A public holiday that falls on the 15th day of the waxing moon in the 6th lunar month, this day commemorates the date of the Buddha's birth, enlightenment and parinibbana, or passing away. Activities are centered around the wát, with candle-lit processions, much chanting and sermonizing.

Mid May-Mid June
Phi Ta Khon Festival - One of the wildest in Thailand, this is an animist-Buddhist celebration held in Loei's Dan Sai district in which revellers dress in garish 'spirit' costumes, wear painted masks and brandish carved wooden phalli. The festival commemorates a Buddhist legend in which a host of spirits (phĭi) appeared to greet the Buddha-to-be upon his return to his home town, during his penultimate birth.
Rocket Festival - In the North-East, villagers craft large skyrockets of bamboo which they then fire into the sky to bring rain for rice fields. This festival is best celebrated in the town of Yasothon, but is also good in Ubon Ratchathani and Nong Khai. It's known in Thai as Bun Bang Fai.
Royal Ploughing Ceremony - To kick off the official rice-planting season, the king participates in this ancient Brahman ritual at Sanam Luang (the large field across from Wat Phra Kaew) in Bangkok. Thousands of Thais gather to watch, and traffic in this part of the city comes to a standstill.

July
Asalha Puja (àsăanhà buuchaa) - This festival commemorates the Buddha's first sermon.
Khao Phansa (khâo phansăa) - Khao Phansa (lent candle festival) is celebrated in the north-east by parading huge carved candles on floats in the streets. A public holiday and the beginning of Buddhist 'lent', this is the traditional time of year for young men to enter the monkhood for the rainy season and for all monks to station themselves in a monastery for the three months. It's a good time to observe a Buddhist ordination.

August
Queen's Birthday - This public holiday is celebrated on 12 August. In Bangkok, Thanon Ratchadamnoen Klang and the Grand Palace are festooned with colored lights.

September
Narathiwat Fair - An annual week-long festival (last week of September) celebrating local culture in Narathiwat Province with boat races, dove-singing contests, handicraft displays, traditional southern Thai music and dance. The king and queen almost always attend.
Diving Buddha Image Festival - Besides the ceremony of diving Buddha image, all Buddhist enthusiasts will witness the procession that is held in respect to Maha Dhammaraja Buddha Image, ritual dances, merry-making, local performances at Muang District of Petchaburi Province.

Late September-Early October
Vegetarian Festival - A nine-day celebration in Trang and Phuket during which devout Chinese Buddhists eat only vegetarian food. There are various ceremonies at Chinese temples and merit-making processions that bring to mind Hindu Thaipusam in its exhibition of self-mortification. Smaller towns in the south such as Krabi and Phang-Nga also celebrate the veggie fest on a smaller scale.

October
Chak Phra Festival – Local people of Surat Thani Province celebrate the end of the three month Buddhist lent by making procession that imitates the hauling of Buddha image from Tapi River in ancient time. A long tailed boat race is also organized during the festival.
Kathin (thăwt kàthĭn) - A month at the end of the Buddhist lent during which new monastic robes and requisites are offered to the Sangha (monastic community). In Nan Province, longboat races are held on the Mae Nan (Nan River).

November
Loi Krathong - On the proper full-moon night, small lotus-shaped baskets or boats made of banana leaves containing flowers, incense, candles and a coin are floated on Thai rivers, lakes and canals. This is a peculiarly Thai festival that probably originated in Sukhothai and is best celebrated in the North. In Chiang Mai, where the festival is called Yi Peng, residents also launch paper hot-air balloons into the sky. At the Sukhothai Historical Park there is an impressive sound-and-light show held at this time.
Surin Annual Elephant Roundup - Held on the third weekend of November, Thailand's biggest elephant show is pretty touristy these days. If you have ever had the desire to see a lot of elephants in one place, then here's your chance.

December
King's Birthday - This holiday is celebrated with some fervor in Bangkok. As with the queen's birthday, it features lots of lights and other decorations along Thanon Ratchadamnoen Klang. Some people erect temporary shrines to the king outside their homes or businesses.