The Western Carpathians are an arc-shaped mountain range, the northern branch of the Alpine-Himalayan fold and thrust system called the Alpide belt, which evolved during the Alpine orogeny. In particular, their pre-Cenozoic evolution is very similar to that of the Eastern Alps, and they constitute a transition between the Eastern Alps and the Eastern Carpathians. Many aspects of the geological structure of the Western Carpathians have not been completely studied and are subject to ongoing research and debate. The appropriate classification of a number of specific is still not clear.