There are a lot of holidays in Cambodia. This year there's 24 public holidays! That's 24 WORK days of... no work! Knowing exactly when the holidays occur isn't as easy as it may seem, but the best source I've found to stay up-to-date on Cambodian holidays is
http://www.mfaic.gov.kh/e-visa/info_holiday.aspx
Date in 2008 Holiday Name
1 Jan. 1 Tue International New Year's Day
2 Jan. 7 Mon Victory Day over the
Genocidal Regime
Feb. 21 Thu Meaka Bochea Day
(Unofficial holiday)
Mar. 8 Sat International Women's Rights Day
3 Mar. 10 Mon Women's Rights Day Holiday
(Observed)
Apr. 13 Sun Cambodian New Year
4 Apr. 14 Mon Cambodian New Year Holiday
5 Apr. 15 Tue Cambodian New Year Holiday
6 Apr. 16 Wed Cambodian New Year Holiday
7 May 1 Thu International Labour Day
8 May 13 Tue King Norodom Sihamoni's Birthday
9 May 14 Wed King's Birthday Holiday
10 May 15 Thu King's Birthday Holiday
11 May 19 Mon Visakh Bochea Day (Buddha Day)
12 May 23 Fri Royal Ploughing Ceremony
(Pithi Chrat Preah Neanng Korl)
13 Jun. 18 Wed King Mother's Birthday
(Norodom Monineath)
14 Sep. 24 Wed Constitution Day
Sep. 28 Sun Bonn Phchum Ben (Ancestors' Day)
15 Sep. 29 Mon Bonn Phchum Ben Holiday
(Observed)
16 Sep. 30 Tue Bonn Phchum Ben Holiday
17 Oct. 1 Wed Bonn Phchum Ben Holiday
18 Oct. 29 Wed King's Coronation Day
(Norodom Sihamoni)
29 Oct. 31 Fri King Father's Birthday
(Norodom Sihanouk)
Nov. 9 Sun Independence Day
20 Nov. 10 Mon Independence Day Holiday
(Observed)
21 Nov. 11 Tue Bonn Om Touk (Water Festival)
22 Nov. 12 Wed Bonn Om Touk (Water Festival)
23 Nov. 13 Thu Bonn Om Touk (Water Festival)
24 Dec. 10 Wed International Human Rights Day
Many of these holidays are Buddhist religious festivals, which are based on the lunar calendar and the dates change from year to year... so be careful to always check for the current year's holiday dates.