Visa Exemption
Visitors to Vietnam must obtain a visa from one of the Vietnamese diplomatic missions unless they come from one of the visa exempt countries or countries eligible for electronic visas
https://visatovietnam.net.vn/exemption-of-entry-visa-to-vietnam.html
Holders of Certificates of Visa Exemption do not require a visa regardless of nationality. A Certificate of Visa Exemption is valid for up to 5 years or up to 6 months before the passport expiration date (whichever is shorter). This is available for Vietnamese residing abroad or spouses or children of Vietnamese citizens or Vietnamese residing abroad.
The exemption is valid for up to 180 consecutive days of stay. There is no limit placed on the number of entries or exits during the stay or minimum waiting time needed in between each 180 days of stay.
https://visatovietnam.net.vn/5-years-vietnam-visa-exemption.html
Phú Quốc Island
Travellers who are not exempted from visa requirements can visit Phu without a visa for up to 30 days. They must arrive at Phú Quốc directly from a third country, or from airports in Hanoi or Ho Chi Minh City where they will clear immigration and proceed to the domestic terminals.
https://visatovietnam.net.vn/phu-quoc-visa-policy.html
Transit
Passengers of any nationality may transit through Vietnam by air without a visa for less than 24 hours providing that they do not intend to leave the sterile transit area. Staying overnight in the transit lounge is permitted
E-visa
Vietnam has introduced a pilot electronic visa system on 1 February 2017 The e-visas have a cost of US$25 and are granted for single entry visits for up to 30 days to nationals of the following 81 eligible countries and territories
https://visatovietnam.net.vn/vietnam-e-visa.html
On arrival visa
Holders of a visa letter issued and at the international airport by the Vietnamese Immigration Department can obtain a visa for a maximum stay of 1 or 3 months
https://visatovietnam.net.vn/all-of-frequently-asked-questions-about-visa-on-arrival.html
APEC Business Travel Card
Holders of passports issued by the following countries who possess an APEC Business Travel Card(ABTC) containing “VNM” on the back of the card can enter visa-free for business trips for up to 60 days.