The pursuit of the well-being of individuals, citizens, and nations is an evaluative measure of how a society functions. What well-being means and how well-being might be achieved is therefore contested and subject to debate. Similarly, research and policy on children’s well-being (CWB) is characterised by multiple interpretations and approaches. The ambiguous nature of the term has resulted in research on CWB involving a diverse range of academic fields. To understand the various traditions in CWB research, it is important to consider the main approaches in the field, the objective and subjective well-being (SWB) approaches. This entry reviews the main philosophical foundations of well-being research to demonstrate the emergence of SWB approaches as a dominant approach to understanding CWB. This entry also examines some critiques ...