Digitized historical newspaper databases offer a valuable research tool. A rapidly expanding set of studies use these databases to address a wide range of topics. We review this literature and provide a toolkit for researchers interested in working with historical newspaper data. We provide a brief description of the evolution of historical newspapers, focusing on aspects that are likely to have implications for the design of empirical studies. We then review the main databases in use. We also discuss some key challenges in using these data, most importantly the fact that even the most extensive datasets contain only a selected sample of the universe of historical newspaper articles. We offer tools for evaluating the comprehensiveness of available newspaper datasets, show how to assess potential identification concerns, and suggest some solutions.