This chapter outlines different approaches to measuring outcomes for children with an acquired brain injury (ABI). The chapter seeks to give the reader a thorough, critical overview of current approaches and models in common use across rehabilitation settings in the UK. It covers some of the philosophical, political, societal and clinical influences that shape our approach to defining and measuring outcomes. Key issues such as measuring complexity, the importance of being collaborative, child-centred and attending to individual nature of each child’s rehabilitation journey are discussed. More in-depth discussion of the outcomes database held by the authors’ organisation and a practice example illustrate the approach taken by the authors in clinical work. A critique of the field and challenges remaining conclude the chapter.