Instrumental neutron activation analysis (INAA) is known to be well suited for provenance determinations of ceramics, since more than 25 minor and trace elements can be measured with precisions high enough to discriminate between different pottery production workshops. INAA-data are presented for more than 1500 shards, mostly wasters, produced in different places such as Brüggen/Elmpt, Brunssum/Schinveld, Frechen/Cologne, Höhr-Grenzhausen, Mayen, Paffrath, Pingsdorf/Brühl, Raeren and Siegburg, to name only the most important earthen and stoneware production centres of the Rhine area in medieval and post medieval times. It turned out, that the wares of these different centres, although by archaeological criteria often very similar, can be clearly recognized by INAA. This large reference databank can now be used to determine export pieces from these centres and to trace trade relations in the Middle Ages. An example of a provenance determination of questionable finds of Pingsdorf and Paffrath Ware from Emden is given.