Specimen database of the Natural History Museum Rotterdam. The total collection is estimated to hold 420.000 specimens, of which over 85% are digitized at the specimen level and contained in this dataset. Arthropods (56%; mostly European) and molluscs (30%; worldwide recent specimens, fossil specimens from North-West Europe) make up the bulk of the collection. Chordates make up 9% of the collection and include a significant amount of fossil terrestrial and marine vertebrates from the Netherlands and the southern North Sea, while recent specimens predominantly originate from the Netherlands. Plants make up 5% of the collection and originate almost exclusively from the Netherlands. The collections of other taxonomic groups, e.g. Fungi and various marine invertebrates, are small, but do contain well documented interesting records. The dataset can also be accessed through the GBIF hosted portal at https://specimens.hetnatuurhistorisch.nl/.