For an exhaustive list of events beyond those listed here, check http://events.frommers.com, where you'll find a searchable, up-to-the-minute roster of what's happening in cities all over the world.
International New Year's Day. Your standard countdown and party, sans Dick Clark. January 1.
Liberation Day. This holiday commemorates the fall of the Khmer Rouge in 1979 and honors those lost during the regime's rule and subsequent wars. January 7.
Chinese New Year. Chinese New Year is not an official holiday in Cambodia but is widely celebrated anyway, primarily by those of Chinese descent and ethnic Vietnamese. February 14, 2010; February 3, 2011.
Meak Bochea Day (Magha Puja Day). Takes place on the full moon to commemorate the speech given by the Lord Buddha to 1,250 enlightened monks who had gathered with no organization or prior warning. In the evening, people visit the temple to make offerings. February 21, 2010; February 19, 2011.
International Women's Day. This day is significant in Cambodia, and raises awareness concerning gender issues. There are often parades with floats in major towns. March 8.
Khmer New Year (Chaul Chhnam Thmey). Along with Ph'chum Benh and the Water Festival, Khmer New Year is one of the most important and popular holidays of the year, celebrated for 3 days in mid-April. The festival is all about water in daily life, and during this festival you will experience the reality of water over and over again (though unlike in neighboring countries, the Cambodian authorities have controlled it from becoming too out of hand). April 14 to April 16, 2010; April 13 to April 15, 2011.
International Labor Day. This is a relatively quiet holiday, where labor unions will sometimes organize events. May 1.
Birthday of the King. Born in 1953, this day celebrates the birthday of the present king who has been on the throne since 2004 when his father, King Sihanouk, abdicated in his favor. May 13 to May 15.
Royal Plowing Ceremony (Bonn Chroat Preah Nongkoal). This marks the start of the rainy season and the planting season. In a ceremony led by the king, elaborately decorated sacred cows plow a symbolic furrow and are then led to trays containing rice, corn, beans, and other foods. These ceremonies are held next to the Royal Palace. May 23, 2010; 2011 dates to be confirmed by astrologers.
Visaka Bochea Day. This festival celebrates the birth, enlightenment, and death of the Lord Buddha. It is held on the 15th day of the sixth lunar month. Candlelit processions take place in the evening. Late May.
Birthday of the Former Queen. Celebrates the birthday of the Queen Mother, Norodom Monineath Sihanouk, wife of the former king who abdicated in 2004. June 18.
Constitution Day. In 1993 the new constitution was adopted on this day. September 24.
Bonn Pchum Ben. During this period, Khmer people make offerings to the monks in order to gain merit. It is a time to honor the spirits of ancestors. People travel to pagodas to make offerings of food, incense, and money to help ease the burden of the spirits. Late September to early October.
Coronation Day. Anniversary of the coronation of King Norodom Sihamoni. The palace is lit up beautifully at night. October 29.
Birthday of the King Father, Holiday for His Majesty King Father Norodom Sihanouk. October 31.
November Water Festival. This celebrates the reversing of the current in the Tonle Sap River and marks the beginning of the fishing season. Dramatic longboat races are held in Phnom Penh with teams coming from all around the country. The city fills up with droves of visitors from the provinces. Dates are subject to change. November 19 to November 21, 2010.
Independence Day. Marking independence from France, on this day the king makes a visit to the Independence Monument on Norodom Boulevard. November 9.
Human Rights Day. In a country where human rights abuse has been an issue, this day observes the Universal Declaration of Human Rights. Cultural events are held at the National Stadium in Phnom Penh. December 10.