Nationals of the United Kingdom and a select number of European countries can enter Vietnam without a visa. This 45-day visa exemption is only valid for for single and multiple entry arrivals and is applicable to all border arrivals (regardless of whether you arrive by air or land). Your passport must be valid for at least 6 months following your date of arrival in Vietnam and have at least two blank pages.
For all other nationalities and anyone staying longer than 45 days, a visa is required. Your visa must be arranged in advance of travelling to Vietnam.
Citizens of 80 countries (including much of Europe, USA, Canada, New Zealand) can apply for an e-visa online. The cost is $25 per person and it is valid for 90 days for single and multiple entry arrivals. You can find more information and apply on the official visa website. This visa will allow multiple entries into Vietnam.