Historic herbaria can provide a wealth of information on a diversity of topics, including the past occurrence of plants, their abundance, names and uses. The collection of Naturalis Biodiversity Center in Leiden, the Netherlands, contains two book herbaria by Jacob Breyne (1637–1697) of Danzig. These herbaria, dated 1659 and 1673, contain a total of 105 specimens in various states of intactness, and with or without original labels. The identity of the specimens in the Leiden Breyne herbaria had not been completely assessed. Here we discuss the taxa represented within these two historic herbaria as well as the information contained in the handwritten texts within them. The two Breyne herbaria combined were found to contain 62 species, representing 24 plant families. Both herbaria contain several species now rare around Gdańsk, including two species currently considered regionally extinct (Swertia perennis L. and Dactylorhiza viridis (L.) R.M. Bateman, Pridgeon & M.W. Chase). Labels with the specimens give a range of information on the collecting locations, ecology, abundance and/or use of the species. The Leiden Breyne herbaria reveal changes in the flora of northern Poland over the course of three centuries, as well as pre-Linnaean nomenclature, historic uses of plants and (international) correspondence between scientists.