Snowdonia (Welsh: Eryri) is a region in north Wales and a national park of 823 square miles (2,130 km²) in area. It was the first to be designated of the three National Parks in Wales, in 1951.

The English name for the area derives from Snowdon, which is the highest mountain in Wales at 3,560 ft (1,085 m). In Welsh, the area is named Eryri. One assumption is that the name is derived from eryr ("eagle"), but others state that it means quite simply Highlands, as leading Welsh scholar Sir Ifor Williams proved. In the Middle Ages the title Prince of Wales and Lord of Snowdonia (Tywysog Cymru ac Arglwydd Eryri) was used by Llywelyn ap Gruffudd; his grandfather Llywelyn Fawr used the title Prince of north Wales and Lord of Snowdonia.

Prior to the designation of the boundaries of the National Park, the term "Snowdonia" was generally used to refer to a much smaller area, namely the upland area of northern Gwynedd centred on the Snowdon massif, whereas the national park covers an area more than twice that size extending far to the south into Meirionnydd. This is apparent in books published prior to 1951 such as the classic travelogue Wild Wales by George Borrow (1862) and The Mountains of Snowdonia by H. Carr & G. Lister (1925). F. J. North, as editor of the book Snowdonia (1949), states "When the Committee delineated provisional boundaries, they included areas some distance beyond Snowdonia proper." The traditional Snowdonia thus includes the ranges of Snowdon and its satellites, the Glyderau, the Carneddau and the Moel Siabod group. It does not include the hills to the south of Maentwrog. As Eryri (see above), this area has a unique place in Welsh history, tradition and culture.