The territory of the region is 38,000 km˛, and it comprises almost half of the whole territory of Hungary. The terrain is very varied with gentle hills, valleys, basins, mountains and plains. The main geographical formations are the Transdanubian Medium Mountains, the southern half of the Little Alföld, the Alpokalja, the Transdanubian Hills, and the Mezőföld (part of the Great Alföld). The main rivers are the Danube, Drave, Rába, Zala, and Kapos. In the middle of Transdanubia lies the biggest sweet-water lake of Central Europe, the Lake Balaton.
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.
Transdanubia has been one of the most important regions of Hungary since the 11th century. Esztergom has been the ecclesiastical capital of the country since 1001 until today, and Stephen I of Hungary established his royal seat at Székesfehérvár, later the coronation town of the kings. Other important medieval cities were Veszprém, Pécs, Győr and Sopron. After the devastating Mongol invasion (see Mongol invasion of Europe) new castles were built, and King Béla IV of Hungary established a new royal capital at Buda, next to the Danube. The region’s rich medieval heritage is seen everywhere from the little village churches to the old castles, monasteries and town houses.
In the Ottoman era (16-17th centuries) the eastern and southern part of Transdanubia came under Turkish rule. The ever changing border ran along the Transdanubian Medium Mountains and the southern shore of the Lake Balaton. The dangerous border was guarded by frontier-fortresses (végvár), the most important them was Győr and Nagykanizsa. The Asian-style Ottoman rule and the constant war had devastating effects: dozens of villages were destroyed, the population was decimated and parts of the region became almost totally deserted. The territories belonging to the Royal Hungary (except the border regions) were more lucky, because the European-like developments were continous. Here the 17th century was the period of the Catholic Counter-Reformation, the fights for national independence from the Habsburgs and the formation of a new, powerful Catholic aristocracy.
In 1686 the allied Habsburg, Polish and Bavarian army reconquered Buda and terminated the Ottoman rule. In the 18th century the region was slowly rebuilt, and lots of new settlers (Magyars, Germans, Slovaks, Croatians) arrived. Famous baroque castles were built to show the power of the big landowner families, for example the Esterházys in Fertőd and the Festetichs in Keszthely. The baroque townscape of the cities survived until today in Győr, Székesfehérvár, Pécs etc.
In the 19th century Trandanubia underwent a capitalist development. Thanks to the closeness of Austria it became again the richest part of the country, and – at least after the public opinion – more "European" and Western-like than any other region of Hungary. Under the Socialism (1948-1989) new industrial cities were built at Tatabánya, Dunaújváros, Ajka and Komló, and new industries and factories were established, for example Hungary’s only atomic power plant at Paks. After the fall of Socialism, northern Transdanubia was more succesful at adapting to the new economical situation than any other part of Hungary and most of the foreign investment came here to help the radical economical renewal.