Yes, visas are required. You will also need six-months validity on your passport beyond the date you plan to return home in order to enter the country. Your Cambodia visa will be purchased upon arrival either at the airport or immigration office if traveling over land. You will need 2 passport photos and the appropriate visa fee. Volunteers staying less than 2 months we recommend buying a tourist visa, the current fee is $25 per month and is renewable for one month only. Volunteers staying longer than 2 months we recommend buying a business visa, the current fee is $30 for the first month. Business visas can be renewed for periods ranging from 3 to 12 months.