Llangybi (sometimes spelled Llangibby) is a village in Monmouthshire, South Wales. The village lies close to the Usk Valley, and nearby towns and villages include Tredunnock, Llantrisant, Llanllywel, Coed-y-paen and Llandegveth.

The Usk Valley forges a natural route into the Brecon Beacons, the Black Mountains and the interior uplands; its turbulent history attesting to how frequently this area has been disputed. Some of the strongholds of the Celts, the Romans, the Normans, the Marcher Lords and the Welsh Princes are seen along the route.

There are two sites for the remains of Llangybi Castle, sometimes known as Tregrug Castle, both a short distance from the village itself. One, the motte and bailey, is close to Castle Farm, and the other on the wooded hillside close by.

There are few remains of the Llangyby motte & bailey, but history buffs will appreciate the more substantial stone walls and chambers of the later castle to be found on the tree-clad hill above.

Llangybi's parish church, dedicated to St Cybi, has been described as "one of the most interesting in the Usk valley" and "a delight". The tower, nave and chancel all date from the 13th or 14th century, and the church has 17th century internal fittings, including the pulpit, font, and monuments to the local Williams family. There are also wall paintings dating from the late medieval period and the 17th century. St Cybi's Church was restored in 1879, but it retains a medieval nave and fifteenth century chancel. There are records of fragmentary paintings on the walls of the chancel. These formed panels in borders with 'simple floriated pattern in yellow, red and black'. These no longer survive, but were probably post-Reformation in origin. Outside is the site of a traditional well, also named for St Cybi.