Tourism is now a global industry involving hundreds of millions of people in international as well as domestic travel each year. The World Tourism Organization indicated that there were for the first time more than one billion international travellers in 2012. By 2017 this figure had reached 1.39 billion international travellers, which amounts to 15 per cent of the world’s population. Although some of this activity may comprise the same travellers involved in more than one journey per year, and hence the precise scale of tourism as an industry is in some doubt, tens of millions of people globally work directly in the industry and many more are employed indirectly. Hundreds of millions of people are on the receiving end of tourism activity as they live in what are termed destination areas, in supposed ‘host’ populations. Millions of dollars are spent each year on advertising and promoting holidays and tourism products. This chapter presents the factors that have contributed to the growth in the importance of tourism.