Most nationalities entering Vietnam (some ASEAN visitors have exceptions) require a visa. Tourist visas are generally valid for 30 days and can be extended depending on the policy in operation at the time, or converted to business visas, etc at a price. Business visas are necessary if you intend to conduct any business at all, and are generally valid for three to six months. Work permits are required for foreign workers in Vietnam, which involves getting medical checks, police reports from home, etc although some ignore this regulation at their own risk.
Customs limits are 200 cigarettes and one litre of alcoholic beverage (including spirits) per person.
Foreign currency in excess of US$7,000 (£3563) in value must be declared on arrival. Be careful about carrying what the authorities refer to as "culturally offensive" items. These might include foreign DVDs, any anti- government literature (this can be widely interpreted so it’s best to play it safe), pornography, weapons and explosives.