Nahuel Huapi National Park (Spanish: Parque Nacional Nahuel Huapi) is the oldest national park in Argentina, established in 1922 as Parque Nacional de Sud and reconfiguered in 1934. It surrounds Nahuel Huapi Lake in the foothills of the Patagonian Andes. The largest of the national parks in the region, it has an area of 7,050 km² (2,720 sq mi), or nearly 2 million acres. Its landscapes represent the north Patagonian Andean Zone consisting of three types, namely, the Altoandino (with perpetual snow above an altitude of 1,600 metres (5,200 ft)), the Andino-Patagónico (in the lower reaches of the hills) and the Patagonian Desert. It also represents small parts of the Valdivian Rainforest.

The park and the reserve lie at an altitude of 720–3,574 metres (2,362–11,726 ft), and are designated under IUCN management categories II (National Park) and IV (Management Reserve). The park is completely protected while the reserve is partially protected. The national park is dominated by the high mountain chain of the Andes, many lakes, rapid rivers, waterfalls, snow-clad peaks, glaciers and extensive forests. It is bordered by Chile on its western side.