Cambodia Visa and Passport Requirements

Passports: 
A passport valid for six months is required for entry into Cambodia.
Visas: 
Visas are required by all nationals referred to in the chart above. You can obtain these in advance or on arrival at most ports of entry.
Visa note: 
Postal applications should included a self-addressed envelope for the return of passports. You must provide your flight details or travel itinerary with your visa application.
If planning on obtaining a visa on arrival, it's advisable to check with the consulate to make sure your port of entry issues visas.
Nationals of Australia, Austria, Belgium, Canada, Denmark, Finland, France, Germany, Greece, Ireland, Italy, Luxembourg, the Netherlands, Portugal, Spain, Sweden, the UK and the USA are also eligible to apply for an ACMECS visa, which is a 90-day joint visa allowing entry to Thailand and Cambodia. It's only really worth obtaining this visa if you're planning on spending more than 30 days in Thailand however, as nationals of these countries can travel visa-free to Thailand for visits of 30 days or less.
Nationals not referred to in the chart above are advised to contact the embassy to check visa requirements.
Overstaying is serious and you’ll be detained until a fine is paid.

Types and cost: 
Tourist (single-entry): £15; business (single-entry): £20; tourist e-Visa (single-entry): US$37.
Tourist visa on arrival: US$30; business visa on arrival: US$35 (payable in US Dollars only). Bring two passport photos.
Visitors can apply for an electronic visa (e-Visa) online through the Cambodian Ministry of Foreign Affairs & International Cooperation (www.evisa.gov.kh). It’s advisable to apply for this at least two weeks before your departure. It is possible to change a departure date after you have applied for a visa, as long as it is before the visa expiry date. You can only use an e-Visa at certain border crossings, so check in advance that it will be valid at your port of entry.
If you apply for an ACMECS visa from the Cambodian Embassy, you pay the usual tourist visa fee for Cambodia then pay Thailand's tourist visa fee at the international border.
Validity: 
All visas are valid for 30 days and must be used within three months of the date of issue.
The ACMECS visa is valid for 90 days from the date of issue, allowing up to 60 days in Thailand and up to 30 days in Cambodia.

Application to: 
Consulate (or consular section of embassy), online (see above) or on arrival.
Working days: 
Visas for Cambodia typically take five working days if you apply in person or six working days for postal applications. e-Visas are issued within three working days, with the visa delivered electronically to the applicant's mailbox.
Extension of stay: 
Extensions of up to one extra month for tourist visas, or one, three, six or 12 months for business visas (which can be multiple-entry) may be granted by the Immigration Department in Phnom Penh.
Entry restrictions: 
Pets require a microchip, a rabies vaccination certificate and a vet health certificate to travel to Cambodia.
Embassies and tourist offices
British Embassy in Cambodia 
Telephone: (0) 23 427 124. Website: http://www.ukincambodia.fco.gov.uk Opening times: Mon-Thurs 0815-1645, Fri 0815-1315 (office); Mon-Fri 0830-1130 (consular). 
Embassy of Cambodia in the USA 
Telephone: (202) 726 7742/7824. Website: http://www.embassyofcambodia.org Opening times: Mon-Fri 0900-1200 and 1400-1700. 
Royal Embassy of Cambodia in the UK 
Telephone: (020) 8451 7850. Website: http://www.cambodianembassy.org.uk Opening times: Mon-Fri 0930-1630 (general); Mon-Fri 0930-1230 (consular section).