Cardigan Bay (Welsh: Bae Ceredigion) is a large inlet of the Irish Sea, indenting the west coast of Wales between the Lleyn and Pembrokeshire peninsulas.

Much of the coast surrounding the bay is fertile farmland, dotted with towns and seaside resorts such as Fishguard, New Quay, Aberystwyth, Barmouth and Pwllheli on the Cambrian Coast. Major rivers flowing into the bay include the Teifi, Rheidol, Dyfi and Mawddach. The northern part of the bay is known as Tremadog Bay.