Tourism is travel for recreation, leisure, religious, family or business purposes, usually for a limited duration.

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

Tourism has become a popular global leisure activity. Tourism can be domestic or international, and international tourism has both incoming and outgoing implications

The World Tourism Organization reports the following ten destinations as the most visited in terms of the number of international travellers in 2014.

The World Tourism Organization (UNWTO) forecasts that international tourism will continue growing at the average annual rate of 4%.

Tourism as a global phenomenon shows no signs of substantially abating in the long term. It has been suggested that travel is necessary in order to maintain relationships, as social life is increasingly networked and conducted at a distance.

For many people vacations and travel are increasingly being viewed as a necessity rather than a luxury, and this is reflected in tourist numbers recovering some 6.6% globally over 2009, with growth up to 8% in emerging economies.

United Nations classified 3 forms of tourism in 1994 in its Recommendations on Tourism Statistics as follows:
Domestic tourism, involving residents of the given country travelling only within this country;
Inbound tourism, involving non-residents travelling in the given country;
Outbound tourism, involving residents travelling in another country.

UN also derived different categories of tourism by combining the 3 basic forms of tourism:
Internal tourism, which comprises domestic tourism and inbound tourism;
National tourism, which comprises domestic tourism and outbound tourism;
International tourism, which consists of inbound tourism and outbound tourism.

Prerequisites of tourism
Before people are able to experience tourism they usually need at least:
Disposable income, i.e. money to spend on non-essentials
Leisure time

Tourism infrastructure, such as transport and accommodation
Individually, sufficient health is also a condition, and of course the inclination to travel. Furthermore, in some countries there are legal restrictions on travelling, especially abroad.

Certain states with strong governmental control over the lives of citizens (notably established Communist states) may restrict foreign travel only to trustworthy citizens. The United States prohibits its citizens from travelling to some countries, for example, Cuba.