The Arpa (Armenian: Արփա; Azerbaijani: Arpaçay) is a river that flows through Armenia and Azerbaijan.

Originating in Armenia's Vayots Dzor province (marz), it is a left tributary of the Aras.

It is 128 km (80 mi) long, and has a drainage basin of 2,630 km2 (1,020 sq mi).

[1] It runs through many cities and towns, including Jermuk, Vayk, Yeghegnadzor, Areni, and then reaches Azerbaijan's Nakhchivan exclave, flowing through Oğlanqala, Siyaqut and Qışlaqabbas.