Metadata are data that define or describe other data. Metadata are essential for interpreting data and making meaningful comparisons over time and between countries. This is particularly so for reporting on Millennium Development Goal (MDG) indicators, which often have multiple data sources and typically attract a wide audience of users who may have limited background in interpreting statistics. MDGs are monitored at the national and international level. Discrepancies exist between data used nationally and internationally. Dissimilarities in data within and between countries may reflect real differences or be due to varying definitions, estimation and calculation methods or data collection and compilation issues. Metadata on definitions, methodology and primary data sources can explain these differences and evaluate the comparability of data between countries. However, the work on the UNECE database has revealed that the metadata provided in official national and international MDG publications is insufficient. It was therefore decided to produce this guide to presenting metadata with examples from the UNECE region. It aims to provide guidance to all those who produce, analyze or publish data. As measurement issues vary from indicator to indicator, different metadata are needed. Fourteen MDG indicators were carefully chosen to reflect the diversity of metadata requirements. Depending on the type of publication and the target audience, the metadata that is mandatory, conditional or optional differs. Recommendations and examples of current practices in metadata presentation are provided for each of the selected indicators. The examples are based on MDG indicators, but the guidelines are applicable to any statistical data. The guide will therefore remain relevant also after the target year of 2015 of the MDGs.