Globally, tourism has shown a steady increase over the last two or three decades, transforming the touristic activities into a real industry. In the new millennium, we have witnessed a continuous growth of interest in the way people spend their leisure time. There is also great interest in the development of what people “consume” during these periods of free time, especially in times dedicated to travel and holidays. With the growth of leisure time, accompanied by a better living standard, the tourism demand has increased. On a global level, we can see an improvement of the revaluation of leisure time and the diminution of the time spent working, fact which generated the engagement in a new form of consumption such as tourism. This article provides an overview of tourism, based on the following aspects: tourism-a major leisure activity, the necessity to measure tourism, tourism statistics, the importance of tourism at a global scale. We have identified and explained the factors that determine the development of tourism, focusing on the economic, demographic and social ones.