This article first provides an overview of the part that secondary data analysis plays in the field of family studies in the early 21st century. It addresses changes over time in the use of existing omnibus data sets and discusses their advantages and disadvantages. The second part of the article focuses on the elements that make a study a "family" study. It describes sources of existing data and the process of selecting a data set. The third part presents special issues and concerns in using existing data, and the fourth part addresses the future of secondary data analysis in the field of family research.