Alltwen (or Allt-wen; translates to "white wooded slope") is a village in the Swansea Valley (Welsh: Cwmtawe) in Wales.

Alltwen forms part of the community of Cilybebyll and is administered separately from adjoining Pontardawe on the opposite bank of the River Tawe.

Allt-wen is an electoral ward of Neath Port Talbot county borough and is a part of the community of Cilybebyll.

The ward is bounded by Trebanos and Pontardawe to the northwest; Rhos to the northeast; Bryn-côch North to the southeast; Dyffryn to the south; and Clydach (in Swansea) to the southwest.

Occupying a strip of land in the northwest of the ward is Alltwen village, which is part of the built-up area surrounding Pontardawe.