As part of its flagship educational study--the Programme for International Student Assessment (PISA)--the Organisation for Economic Co-operation and Development (OECD) has undertaken extensive work to create an internationally relevant composite indicator aimed at measuring socioeconomic background. However, the degree to which a single measure of socioeconomic background is reliable and valid for all participating countries is not widely discussed. To fill this gap, the authors examine the home possessions index, which is a key component of PISA's socioeconomic indicator, and highlight a number of issues surrounding this index. In particular, they take a psychometric approach to investigating the reliability and some facets of the validity of the home possessions index in a number of participating PISA countries. Their findings suggest that there are notable concerns with the current index, including highly variable reliability by country, poor model-to-data consistency on a number of subscales, and evidence of poor cultural comparability. They couch their discussion in the context of educational and policy research and propose one possible method for improving these measures for participating countries.