If we consider the 50 states having ratified the European Cultural Convention of the Council of Europe or the member states of the European Union, the multiple and divergent nature of the realities, theories, concepts and strategies underlying the expression "youth work" becomes evident. Across Europe, youth work takes place in circumstances presenting enormous differences with regard to opportunities, support, structures, recognition and realities, and how it performs reflects the social, cultural, political and economic context, and the value systems in which it is undertaken. By analysing theories and concepts of youth work and by providing insight from various perspectives and geographical and professional backgrounds, the authors hope to further contribute to finding common ground for - and thus assure the quality of - youth work in general. Presenting its purified and essential concept is not the objective here. The focus rather is on describing how to "provide opportunities for all young people to shape their own futures", as Peter Lauritzen described the fundamental mission of youth work. The best way to do this remains an open question. This Youth Knowledge book tries to find some answers and strives to communicate the strengths, capacities and impact of youth work to those within the youth sector and those beyond, to those familiar with its concepts and those new to this field, all the while sharing practices and insights and encouraging further reflection.