No modern state can exist in the long term without effective taxation. Recent research emerging from close collaboration of academics with tax authorities has shed new light on how states can build such tax capacity. Using both randomized and natural experiments, these partnerships have not only opened access to new types of data but have also stimulated new perspectives and research questions. While much of research in public finance has historically assumed that a tax in the law is a tax that is collected, exciting new research takes an empirical look inside the black box of tax administration. It addresses issues ranging from the role of information and digitalization to taxpayer behavior or to the link between taxation and citizens’ relationship to the state. This article provides a brief overview of some of this research, as well as practical advice for those interested in implementing research in partnership with tax authorities or other large public entities.