The subsurface is important. It provides us with energywater and minerals, resources of which are indispensable national assets that need to be managed carefully. And we usually forget that we live on top of it – the subsurface is part of our living environment. Its properties and processes determine ground stability, the extent to which mining activities may have side effects such as subsidence and induced earthquakes, and how and in what way soils and groundwater are vulnerable to human impact. And we use the subsurface for storage or disposal: of thermal energy, natural gas, CO2 and a variety of wastes. It goes without saying that our subsurface needs to be terra cognita, and TNO Geological Survey of the Netherlands exists for that very purpose!