Seine-Saint-Denis (French pronunciation: [sɛn sɛ̃ d(ə)ni] ⓘ) is a department of France located in the Grand Paris metropolis in the Île-de-France region.

In French, it is often referred to colloquially as quatre-vingt treize or neuf trois ("ninety-three" or "nine three"), after its official administrative number, 93.

Seine-Saint-Denis and two other small departments, Hauts-de-Seine and Val-de-Marne, form a ring around Paris, known as the Petite Couronne ("little crown").

It was formed from the part of the (hitherto larger) Seine department to the north and north-east of the Paris ring road (and the line of the old city walls), together with a small slice taken from Seine-et-Oise.

A commune of Seine-Saint-Denis, Clichy-sous-Bois, was the scene of the death of two youths which sparked the nationwide riots of autumn 2005.

Population development since 1881:An education study confirmed falling levels of literacy in the area, where the percentage of pupils who had 25 errors or more increased from 5.4% in 1987 to 19.8% in 2015.