An explosion of new data sources describing historical family composition is opening unprecedented opportunities for discovery and analysis. The new data will allow comparative multilevel analysis of spatial patterns and will support studies of the transformation of living arrangements over the past 200 years. Using measurement methods that assess family choices at the individual level and analytic strategies that assess variations across space and time, we can dissect the decline of patriarchal family forms in the developed world, and place Northwestern Europe and North America in global comparative context.