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.
In 2010, international tourism reached US$919B, growing 6.5% over 2009, corresponding to an increase in real terms of 4.7%. In 2010, there were over 940 million international tourist arrivals worldwide. By 2016 that number had risen to 1,235 million, producing 1,220 billion USD in destination spending. The COVID-19 crisis had significant negative effects on international tourism significantly slowing the overall increasing trend.
International tourism has significant impacts on the environment, exacerbated in part by the problems created by air travel but also by other issues, including wealthy tourists bringing lifestyles that stress local infrastructure, water and trash systems among others.