Chapter 1 examines the theoretical basis of the best interests principle. This chapter examines the implications and demands of the principle, and it explores how the principle is to be applied. In line with the guidance provided by the Committee on the Rights of the Child, the best interests principle is understood to be a right, the content of which is guided by reference to the other rights contained in the UNCRC. The advantage of this approach is that it allows the best interests principle to be realised in a structured manner, namely one that is guided by the UNCRC. The chapter provides further nuance to the best interests principle by identifying a new conceptual framework for its application. This framework is designed to overcome the perceived deficiencies of the principle. The framework not only is largely based on the guidance of the Committee, but also suggests that social science literature should be incorporated into the best interests assessment to provide broader guidance about what is ‘best’ for children in particular situations.