The first phase (2000-2003) of Young Lives was supported by the UK Department for International Development (DFID) with the purpose 'to measure and find out about what happens to children born into poverty in the millennium'. This paper sets out the conceptual framework that underpins the project and was developed prior to the design of the data collection instruments in Phase 1. Section 2 gives a brief overview of approaches to conceptualising childhood and the concept of childhood adopted by Young Lives. Section 3 considers what is meant by childhood poverty, and the reasons why it should be a focus of study in its own right. Section 4 outlines the framework for analysing the causes and consequences of childhood poverty and the reasoning behind it.