The River Afan (sometimes anglicized as Avon) is a river in south Wales whose valley formed the territory of the medieval Lords of Afan. The town of Aberavon grew up on the banks of the river, and was later subsumed by the larger centre of population known as Port Talbot.

The river runs in a more or less south-westerly direction parallel to the River Neath with which it shares its western watershed. In the east it borders the River Kenfig and then the River Llynfi a tributary of the River Ogmore. At its source, it also shares a watershed with the Rhondda Fach, a tributary of the River Taff.

For much of the 19th century and the first half of the 20th century, the River Afan was severely polluted by the coal and iron industry. With the decline in the coal industry, the quality of the river improved in the 1960s and 1970s so that some salmon and sea-trout started to return to the river to spawn. This work was driven by an enormous commitment by the Afan Valley Angling Association led by Mr Glan Williams. A number of weirs on the river, built to sustain the industrial past, had to be made passable to allow fish to ascend the river. This required the creation of fish passes on some weirs such as on the Dock feeder weir and the demolition of others such as at Corlannau weir.

A major tributary, the Afon Pelena, suffered more severely from pollution than the main river because of the sulphur-rich coal produced by the mines in that area. As a result, the abandoned coal mines continued to discharge acid mine drainage rich in iron and highly acidic. This turned the whole river orange down to the confluence of the Pelena with the main river Afan at Pontrhydyfen (the birthplace of Richard Burton). The principal colliery responsible was the Whitworth colliery. This pollution is now much mitigated following extensive work promoted by the Environment Agency in the creation of engineered reed beds to treat the mine drainage.

A small tributary of the Afan, the Nant Ffrwdwyllt, was diverted in the 18th century into the ironworks at Port Talbot to provide a source of water. It remains diverted flowing into the Port Talbot docks before eventually reaching the main river in the return water at the Dock feeder weir. This water too was grossly polluted for many years, principally with cyanide emanating from blast-furnace cooling waters. This had the very visible impact of killing thousands of smolts - the young of sea-trout - returning to the sea. With recent improvements in emission control in the steel making plant, this problem has been abated.

The River passes the Afan Argoed Country Park in its middle reaches.

A motte and bailey castle stood on the banks of the river during the medieval period. No remains are now visible above ground, but the site of the castle is commemorated in local street names.