Guissény (French pronunciation: [ɡiseni]; Breton: Gwiseni) is a commune in the Finistère department of Brittany in north-western France.

To the west, it is limited by the Porz Olier (its eastern tip containing Dibennou and its western Beg ar Skeïz), a small residual marine gulf that was once much larger.

Most of the gulf has been transformed into a polder (La Palud de Curnic, where salt marshes once existed) or pond (Étang du Curnic) due to the construction of a dyke that separates Guissény from Plouguerneau.

To the west of Curnic, the coastal platform is several hundred meters wide and includes a number of emerged rocky islets: Karreg Hir (the Karreg Hir causeway extends northwest to the rocks of Lizenn Du and includes numerous islets emerging at low tide), Golhédoc, Énez Du, Tilloc, and Énez Croaz-Hent (the latter now being linked to the mainland by a dyke).

In 2009, 21.55% of primary-school children attended bilingual schools, where Breton language is taught alongside French.