In 2019, the Financial Intelligence Unit of the Netherlands (FIU-the Netherlands) celebrated its 25th anniversary. This article uses the occasion to reflect on the pivotal role of the FIU in financial surveillance and to describe its core practices of collecting, analyzing, and disseminating financial intelligence. What makes an FIU particularly interesting is that it operates at various intersections: not only on the nexus of finance and security, but also between private and public actors, by transforming unusual transaction information into suspicious financial intelligence. Given this pivotal position of the FIU, it is surprising that little is known about its core activities. Because its practices are often secret and its data are classified as state secrets, its daily operations and operational processes remain obscure. By drawing on interviews, public reports, and an online training programme this article aims to encircle the secrecy, zoom in on the case-study of FIU-the Netherlands and offer a fine-grained analysis of each of the three core FIU activities. Such a case-study is important not only for the study of finance and security as well as financial surveillance, but also for policy makers and the broader public who merit an understanding of how their financial behaviour is being surveilled.