International tourism is tourism that crosses national borders. Globalisation has made tourism a popular global leisure activity. The World Tourism Organization defines tourists as people "traveling to and staying in places outside their usual environment for not more than one consecutive year for leisure, business and other purposes". The World Health Organization (WHO) estimates that up to 500,000 people are in flight at any one time.

Tourism is travel for pleasure, and the commercial activity of providing and supporting such travel. UN Tourism defines tourism more generally, in terms which go "beyond the common perception of tourism as being limited to holiday activity only", as people "travelling to and staying in places outside their usual environment for not more than one consecutive year for leisure and not less than 24 hours, business and other purposes". Tourism can be domestic or international, and international tourism has both incoming and outgoing implications on a country's balance of payments.