The United States’ federal and state governments collect and make available enormous amounts of free, accurate, public data. Using these data can contribute to addressing a variety of challenges researchers face. For example, we describe how applying public data made possible our study of why cities decide to hire lobbyists in Washington, D.C. In most lobbying studies, it is very hard to compare entities who lobby with those who do not because of limited data availability. By merging together public data sets, we were able to study both cities who lobbied and those who did not—avoiding problems of research design validity that arise when one selects cases based on the dependent variable, that is, whether cities lobbied.