There are two major ports of entry of entry by air, the Phnom Penh and Siem Reap International Airports and a large selection of entry points on the borders with Thailand, Vietnam and Laos.
A passport is absolutely essential and you must make sure it is valid for at least another six months beyond the end of your trip in Cambodia. Immigration officials will not issue a visa if your passport is good for less than 6 months.
Visa on Arrival
All travelers can now get a visa on arrival at the international airports and at border crossings with Thailand and Vietnam. It costs US$20 per person and the airport counters are fast and hassle-free. Some people choose to enter on a business visa for US$25.00. While entry at land borders is relatively easy, immigration officials may try to get you to cough up more cash.
You need two color passport-size photos or there is a US$1 fine at the airport and as much as 100 Baht (US$2.85) at the border crossing from Thailand. Citizens from Laos, Malaysia, Philippines and Singapore do not need a visa to enter Cambodia.
Tourist and Business Visas
Ensure there is lots of space left in your passport, especially for those on a long Asian tour. A Cambodian visa can take up a page and while extra pages can be added, many embassies will require a new passport.
A tourist visa lasts for a month, can be extended only once for one month and does not permit re-entry. A business visa is easily extended, can be done several times and indefinitely, and will allow for multiple entries and exits. It can be extended for one month, three months, six months and even for a year. A fine of US$5 a day is imposed for staying beyond the duration of the visa.