St John Ambulance is the name of a number of affiliated organisations in different countries, which teach and provide first aid and emergency medicine and are primarily staffed by volunteers. The associations are overseen by the international Order of St John and its priories (national branches).

The first such organization to be founded was the St John Ambulance Association, which was founded in 1877 in England. Its first uniformed first-aiders were founded in 1887 as the St John Ambulance Brigade. These two have since been merged into a single association. St John Ambulance now have over 40 national organizations, many of which are affiliated with Johanniter International, and over 500,000 volunteers worldwide.

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The Order of St John owns the brand name and logo. Logos may vary in each country but always contain the eight-pointed Maltese Cross as the essential identifier. Like the Order, St John Ambulance associations accept members of all religions. Their geographic organization differs from the Order, and they have to contend with the differing national laws, medical practices and cultures of countries. As a result, the role and organization of St John Ambulance varies by country.