Llanelly (Welsh: Llanelli) is the name of a parish and coterminous community in the principal area of Monmouthshire, within the historic boundaries of Brecknockshire, south-east Wales. It roughly covers the area of the Clydach Gorge. The population of the parish and ward at the 2011 census was 3,899.

The parish encompasses the area surrounding the Clydach Gorge, west of Abergavenny, east of Brynmawr and south of Crickhowell.

Llanelly Hill, Blackrock, Clydach, Maesygwartha and Gilwern are the main settlements in the parish. Llanelly Hill occupies the north-west hilltop of the Clydach Gorge. It developed as a result of coal mining and limestone quarrying for the nearby ironworks including those at Clydach and Ebbw Vale.

Blackrock and Clydach North (also referred to as Cheltenham) were both built up along the turnpike road that ran on the north side of the river between Govilon and Merthyr Tydfil. Clydach South developed on the south side of the river above the ironworks. It climbs the north-west slopes towards Llanelly Hill.

Gilwern is located at the mouth of the River Clydach, where it meets the River Usk. Maesygwartha lies between Clydach and Gilwern along one of the many tramroads in the gorge.

The Church of St Elli dates from the 14th century or earlier. The parish is part of the principal area of Monmouthshire. Historically within Brecknockshire, from the local government reorganisation of 1974 until that of 1996, it lay in the district of Blaenau Gwent, but the electors overwhelmingly voted to be transferred out. The highest part of the parish, in the southwest had previously been transferred into the new urban district of Brynmawr in the 1890s. The Brecon Beacons National Park encompasses the parish and the surrounding area.

The electoral ward of Llanelly Hill is coterminous with the Llanelly community and elects one county councillor to Monmouthshire County Council.

• Sir Henry Bartle Frere (1815–1884), Governor-General of South Africa at the outbreak of the Anglo-Zulu War
• Thomas Phillips (1801–1867), Mayor of Newport during the Newport Rising

Llanelly, a former Welsh gold-mining town near Tarnagulla, Australia

• grid reference SO232148

51°49′35″N 3°06′57″W / 51.82652°N 3.11579°W / 51.82652; -3.11579