The Key register Subsoil (Basisregistratie Ondergrond, BRO) is to become the central database containing all public data on the Dutch subsoil. The BRO Act, which came into effect on 1 January 2018, requires that source data owners provide and use soil and underground data in a digital form. The requirements will be expanded step by step in the next 4 years. The data in this key register have been validated and are of importance for activities like fresh water procurement, underground transport, and mineral mining, but also for activities on the surface, like energy transition, housing construction, and infrastructural projects.