This paper investigates the possibilities for the creation of a global dataset on family and household characteristics. This is done by scrutinizing and comparing two prominent data sources on family system classifications. We first focus on historical data, by comparing Emmanuel Todd's classification of countries by family systems with ethnographic data compiled in George Murdock's Ethnographic Atlas. Qualitative and quantitative tests show that the two datasets frequently agree about family traits. Nonetheless, substantial differences exist that are mostly attributable to the focus of the datasets on different regions, and the difficulties in translating local, descriptive studies to hard data. We therefore emphasize that it is important to know the strengths and weaknesses of the two datasets and emphasize that robustness checks are necessary in empirical research into family characteristics. We also compare these historical data with present-day data. This comparison suggests that family characteristics and the values associated with them can persist over long periods. Auke Rijpma, Utrecht University, Drift 6, 3512BK Utrecht, The Netherlands. Email: a.rijpma@uu.nl Sarah G. Carmichael, Utrecht University, Drift 6, 3512BK Utrecht, The Netherlands. Email: s.g. carmichael@uu.nl We would like to thank Tine De Moor, Jan Kok and Jan Luiten van Zanden for their comments on previous versions of this paper. Additionally we are grateful to Jaco Zuijderduijn, Bastian Mönke-diek, Pim de Zwart, Paul Rotering, Benjamin Guilbert, Christiaan van Bochove, Oscar Gelderblom, Maarten Prak, Selin Dilli, Lotte van der Vleuten, and Kati Buzási for their comments during workshops in April and June 2012. We also thank participants at the WEHC 2012 session 'Marriage patterns, agency in households, and economic growth' and three anonymous referees. Last but not least we thank Jutta Bolt for the underlying data, her patience, and always responding to our numerous email questions.10