Philippine and Malaysian citizens can travel to Cambodia for 21 and 30 days respectively without a visa, but all other nationalities are required to have a visa upon entering Cambodia. Visas are available on arrival at both international airports in Phnom Penh and Siem Reap, and most overland crossings. The official rate is US$20 for a one-month tourist visa and US$25 for a one-month business visa which can be extended multiple times. You will need a passport that is valid for at least the next 6 months and 1 passport photo.
For overland entries, visas are available upon arrival at the Vietnamese (Bavet and Kaam Samnor) and Thai border crossings (Poipet and Krong Koh Kong) but not the Lao crossings (Koh Chheuteal Thom or Dom Kralor). Please note that whatever the border officials might tell you at at the Thai crossings at Poipet and Krong Koh Kong, a tourist visa is still US$ 20. Paying 1,000 baht for a tourist visa or 1,500 baht for a business visa, which is higher than the standard rate elsewhere, will, however, save you some time and hassles, and 100 baht seem to have become a 'standard' unofficial 'facilitation fee'. Border officials may refuse US dollars and request the amount in Thai Baht, but there is no law saying that the official cost of US$ 20 has to be paid in Thai Baht.
Beware of entry scams: do not be scammed by drivers or others who insist you need their help to get a visa, guards claiming there is a fee for a SARS form or immigration police overcharging for the visas. Particularly for the latter two, it is probably more effective to refuse politely, pretend to not understand or ask for a receipt (which they wouldn't be able to produce for false fees) rather than losing your temper or shouting.
Renew your visa through a Cambodia travel agent or the Department of Immigration on Airport Road (Confederation de Russie) opposite.
We suggest you check this information with your relevant government consulate for the most current information regarding Cambodian Visas and Passport requirements for entry.