A passport valid for at least 6 months is necessary for entry to Cambodia.
All non-Cambodian citizens (except citizens of Laos, Malaysia, Philippines, Singapore, and Vietnam) require a visa. Visas can be obtained at any Cambodian embassy or consulate overseas. Visas are also available on arrival by either land or air. Two photos, a valid passport, and $20 are required for a month-long single-entry tourist visa. This can be extended within the country, and is most easily done through travel agents. Business visas are also available. They cost $25, and can be extended for up to a year, with multiple entry.
The simplest way to apply for a visa is online, using the e-visa scheme launched by the Cambodian Ministry of Foreign Affairs and International Cooperation in 2006. Instead of applying through a Cambodian embassy, you simply complete the online application form and pay with your credit card. After receiving your visa through e-mail, print it out and bring it with you for your arrival. To apply for an e-visa, applicants need to have a passport valid for at least 6 months, a recent passport-size photo (JPEG/PNG format), and a valid credit card (Visa/MasterCard). The visa costs $20 and there is a $5 processing fee. It is important to note this visa is only good for arrival at Siem Reap and Phnom Penh international airports and by land from Thailand at Poipet/Aranyaprathet and Koh Kong/Had Lek, and Vietnam at Bavet/Svay Rieng. It is not valid for any other border crossings. To apply for an e-visa, go to www.mfaic.gov.kh.
If traveling overland, be aware that some border posts are run very much as income-producing concerns by those staffing them. There are often superfluous touts pushing to help you complete the process for a fee. You don't need them. The process is simple. At some borders with Thailand, Cambodian immigration will insist you pay in Thai baht because they can make money on the differential on the exchange rate. There is not much you can do about this if you want to get into the country.
Although Cambodia issues visas on arrival at most if not all entry points, the same cannot be said if you are traveling the other way to a neighboring country. Vietnam requires that you have a visa before you travel whether you enter by land or by air, and at the time of writing a visa on arrival is not available when crossing from Cambodia to Laos by land. Thailand allows most nationalities to stay as tourists in the country for 30 days on arrival. At press time this was still true if you arrive by air. In 2008, they reduced the period to 15 days only if you arrive by land. Check with the Thai Embassy or a reputable travel agent if you are traveling on to Thailand from Cambodia and you want to stay in Thailand longer than the allotted time. Requirements are changeable.
Warning: Fake Visas at Poipet -- On the Thai side of the Poipet border you will be harassed by a legion of touts offering to make your Cambodian visa for you. They will charge you more than if you get your visa at the allotted office before Cambodian immigration. In recent months that harassment has turned to veiled menace. Whoever these people are (and they are Cambodians), there is obviously money in what they are doing since they could not operate without the tacit permission of the Thai border police and the Cambodian immigration officials. When I approached the border, they had actually set up an official-looking checkpoint and flagged down my motorcycle as if they were police. All this is a scam. It is perfectly normal and legal to get your visa on arrival at Cambodian immigration once you have exited Thailand. Anyone who tells you otherwise is lying. Many tourists I saw were visibly upset at the intimidation even before they had set a foot on Cambodian soil. Ignore the touts, however insistent they may be.
Visitors who are 18 years or older are allowed to bring into Cambodia 200 cigarettes or the equivalent amount of tobacco, and one opened bottle of liquor and perfume for personal use. Currency in possession must be declared on arrival. Cambodian Customs on the whole are not too fierce.
There are no vaccination requirements on entering Cambodia, but for your own well-being it is wise to get certain vaccinations including hepatitis A, hepatitis B, typhoid, Japanese encephalitis, cholera, rabies, and tetanus. It is also advisable to update your childhood vaccination series for polio, measles, mumps, rubella, and so on, if you are likely to be around children.
Note: This information was accurate when it was published, but can change without notice. Please be sure to confirm all rates and details directly with the companies in question before planning your trip.