This publication contains the proceedings of two UNWTO conferences on "Tourism: a Tool for Sustainable Development in Transitional Economies", held in Belgrade on 20-21 June 2005, and "Impact of European Union Enlargement on Tourism Development in Europe", held in Vilnius, on 1-2 March 2006. There is an overlap between economies in transition and the group of countries that joined the European Union in 2004 and, from the perspective of tourism development, a large group of European countries share similar challenges and opportunities. While Europe is the region that receives the largest number of international tourists and registers the highest amount of receipts from international tourism, there is a great difference between traditional destinations with a long history of tourism development and the countries that recovered independence after the collapse of the Soviet Union. Some countries already undertook major reforms in their political and economic spheres while others are still addressing structural issues inherited from the past. Tourism contributes positively to European integration and at the same time its success depends on the development and modernisation of several economic and social sectors.