This document discusses the importance of reliable data for monitoring progress towards achieving the Millennium Development Goals (MDGs). It outlines how MDG monitoring has driven development policy decisions by generating public support and funding. Disaggregated data has helped identify issues in local areas and among marginalized groups, allowing for effective interventions. The MDG framework has also strengthened statistical capacity and improved data availability in many developing countries. National statistical systems have been able to produce internationally comparable development indicators, and coordination within countries on data collection has improved.