Despite substantial academic and policy interest in well-being there is no universally accepted definition of the concept. In the academic literature, it is used as an over-arching concept to refer to the quality of life of people in society. The purpose of this chapter is to present the findings of the MYWeB project regarding the conceptions of well-being among children and young people and the possible differences among them in four European countries (Portugal, Greece, Slovakia and Estonia). Based on qualitative research which makes the voice of children and young people heard, this chapter represents an important contribution to issues pertaining to the measurement of child well-being. Semi-structured interviews and focus groups with children and young people addresses four questions: How do children and young people understand the concept of well-being? What do they attribute to well-being? Which are the main factors they consider important for their well-being? What are the similarities and differences among the four European countries? Having in mind that in order to organise and conduct a longitudinal survey on children and young people’s well-being the understanding of the concept of well-being is central, this chapter explores the different approaches and understandings of the concept and discuss the obstacles and problems that might arise in such a process.

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