Brecon Beacons National Park, officially named Bannau Brycheiniog National Park (Welsh pronunciation^ⓘ), is a national park in Wales. It is named after the Brecon Beacons (Welsh: Bannau Brycheiniog), the mountain range at its centre. The national park includes the highest mountain in South Wales, Pen y Fan, which has an elevation of 886 metres (2,907 ft).

The national park has a total area of 1,344 square kilometres (519 sq mi). The Brecon Beacons and Fforest Fawr uplands form the central section of the park. To the east are the Black Mountains, which extend beyond the national park boundary into England, and to the west is the similarly named but distinct Black Mountain range. These ranges share much of the same basic geology, the southerly dip of the rock strata leading to north-facing escarpments. The highest peak of the Black Mountains is Waun Fach (811 metres; 2,661 ft), and Fan Brycheiniog (802.5 metres; 2,633 ft) is the highest of the Black Mountain.

The park was founded in 1957 and is the third and most recently designated national park in Wales, after Snowdonia (Eryri) and the Pembrokeshire Coast. It is visited by approximately 4.4 million people each year.

The name Bannau Brycheiniog is first attested in the sixteenth century, and 'Brecon Beacons' first occurs in the eighteenth century as "Brecknock Beacons". Bannau Brycheiniog derives from the Welsh bannau, 'peaks', and Brycheiniog, the name of an early medieval kingdom which covered the area. The English name is derived from the Welsh one; in the eleventh century the town of Brecon is recorded as 'Brecheniauc', which became "Brecknock" and "Brecon".

In a paragraph on Brecknockshire, John Leland's 1536–1539 Itinerary notes that:

Blak Montayne is most famose, for he strecchith, as I have lerned, his rootes on one side within a iiii. or v. myles of Monemuth, and on the other side as nere to Cairmerdin (Carmarthen). Though this be al one montayne, yet many partes of him have sundry names.

Leland ascribes the name "Banne Brekeniauc" to the hills surrounding "Artures Hille" (Pen-y-Fan), also calling the range the "Banne Hilles".

The term "Brecknock Beacons" was used in the eighteenth century and referred to the area around Pen y Fan, which was itself was sometimes called 'the (Brecknock) Beacon'. For instance, Emanuel Bowen's A New and accurate map of South Wales (1729) labels the peak as 'The Vann or Brecknock Beacon', John Clark's 1794 General View of the Agriculture of the County of Brecknock refers to 'the Vann, or Brecknock Beacon, the undisputed sovereign of all the mountains in South Wales', and an 1839 tithe map of Cantref parish labels the mountain simply 'Beacon'. A slightly wider definition was used in 1809 by the Breconshire historian Theophilus Jones, who wrote that 'of the lofty summits of the Brecknock Beacons, that most southwards is the lowest, and the other two nearly of a height, they are sometimes called Cader Arthur or Arthur's chair'. This implies that "Brecknock Beacons" referred to only three summits, including Pen y Fan and Corn Du.