Selzerbeek (or Senserbach, Sinselbeek, Sinselbaach, Selzerbaek) is a river of North Rhine-Westphalia, Germany and Limburg in the Netherlands.

It stretches over approximately 13 kilometres (8 mi) from its source at Aachen to its mouth near Gulpen into the Geul.

From Vaals through Lemiers to Mamelis the Selzerbeek forms the natural border between the Netherlands and Germany.

In this area, it flows to other small streams: the Orsbacher Puetz, the Zieversbach at Holset, the Herman Bach Lemiers and Harleserbach at Harles.

Behind Mamelis flows Selzerbeek by the Netherlands, parallel to Provincial route 278 along the villages Nijswiller, Wahlwiller and Partij until it empties into the Geul (a direct tributary of the Meuse) near Wittem.