Visa to Cambodia can be applied at ports of entry whether you come by air or by land.
Travelers are required to show your phhoto (3x4cm) and their valid passport. The Government Immigration distributes application forms upon arrival.
If you arrive by air at Phnompenh International airport or Siem Reap International airport, it is so simple and just take you few minutes to get visa done. The fee is $30 USD for a 30 day visa (Cash only).

For most visitors to the Kingdom, visa are obtainable upon arrival at both Phnom Penh and Siem Reap International Airports in Phnom Penh and Siem Reap. At land crossing from Thailand, visas are available at Poipet Banteay Meanchey and Cham Yeam (Koh Kong province). Visitors who enter from Vietnam through Bavet (VN: Moc Bai – when you drive from Saigon) or Ka-Om Samnor (VN: Chau Doc -Mostly people come by boat) will need to have already obtained their visas prior to their arrival through a Cambodian Embassy or Consulate overseas. Tourists also can obtain visa through the online E-Visa.

Visa Fees:
Single entry visa fee for tourist (T) (30 days): US$ 30
Single entry visa fee for business (E) (30 days): US$ 35

The entry points to obtain Visa:
Airports:

Phnom Penh International Airport
Siem Reap International Airport

Cambodia-Vietnam border:
Bavet International Check Point (Svay Rieng Province)
Kha Orm Sam Nor International Check Point (Kandal Province)
Koh Rohka International Check Point (Prey Veng Province)
Banteay Chakrey International Check Point (Preyveng Province)
Tropeang Sre International Check Point (Kratie Province)
Prek Chak International Check Point (Kampot Province)
Phnom Den International Check Point (Takeo Province)
Oyadav International Check Point (Rattankiri Province)
Tropieng Phlong International Check Point (Kampong Cham Province)

Cambodia-Thailand border:
Cham Yeam International Check Point (Koh Kong Province)
Poi Pet International Check Point (Banteay Meanchey Province)
Osmach International Check Point (Odor Meanchey Province)
Sihanoukville International Check Point (Sihanoukville Province)
Choam Sanguam International Check Point (Banteay Meanchey Province)
Prum International Check Point (Pailin Province)
Doung International Check Point (Battambang Province)
Preah Vihear International Check Point (Preah Vihear Province)

Cambodia-Lao border:
Dong Krolar International Check Point (Steung Treng Province)
Tropieng Kreal International Check Point (Stung Treng Province)
It is required for the visa applicants to submit passport, application forms, a recent passport-style color photograph, and such other documents as determined by the status of stay.

Tourist & Business Visas:
Visitors from countries not under Visa Exemption Agreements must apply for a Tourists (T) or business (E) visa valid for one month at the points of entry.

Visa (K) can be issued to a Cambodian national entering the Kingdom on a foreign passport. (The applicant has to provide well-documented evidence, such as proof that one’s parents were Cambodian).

Visa Exemption:
The nationals of the Laos, Malaysia, Philippines, Singapore, Vietnam, Thailand, Indonesia, Brunei Darussalam, Myanmar do not need a tourist visa and may stay in Cambodia for 21 and 30 days respectively.

Visa extension:
The tourist (T) and business (E) visas can be extended at the Immigration Department, National Police. The Diplomatic (A), Official (B) and Courtesy (C) visas can be extended at the Consular Department, Ministry of Foreign Affairs. A tourist visa can be extended only once for up to one month (single entry).

A business visa can be extended for:
One month (Single entry)
Three months (Single entry)
Six months (Multiple entry)
One year (Multiple entry)
Overstayers will be fined US$ 10 per day.