Transdanubia (Hungarian: Dunántúl; German: Transdanubien, Polish: Transdanubia; Croatian: Prekodunavlje or Zadunavlje, Slovak: Zadunajsko) is a traditional region of Hungary.
Transdanubia can also refer to the 21st and 22nd districts of Vienna, which are the only ones lying on the left bank (eastern side), of the Danube. See Floridsdorf and Donaustadt respectively.
The borders of Transdanubia are the Danube River (north and east), the Drava and Mura rivers (south), and the foothills of the Alps roughly along the border between Hungary and Austria (west).
Transdanubia comprises the counties of Győr-Moson-Sopron, Komárom-Esztergom, Fejér, Veszprém, Vas, Zala, Somogy, Tolna, Baranya and the part of Pest that lies west of the Danube. (In the early Middle Ages the latter was known as Pilis county.)
This article deals with Transdanubia in this geographical meaning.