Seine was a department of France encompassing Paris and its immediate suburbs. Its capital was Paris and its official number was 75. The Seine department was abolished in 1968 and its territory divided among four new departments.

The Seine department was created on March 4, 1790 as the Paris department In 1795, it was renamed the Seine department Seine River flowing through it.

From 1929 to its abolition in 1968, the department consisted of the city (commune) of Paris and 80 suburban communes surrounding Paris. It had an area of 480 km² (185 sq. miles), 22% of that area being the city of Paris, and 78% being independent suburbs. It was divided into three arrondissements: Paris, Sceaux, and Saint-Denis.

At the first French census in 1801, the Seine department had 631,585 inhabitants (87% of them living in the city of Paris, 13% in the suburbs) and was the second most populous department of the vast Napoleonic Empire (behind the Nord department), more populous than even the dense departments of what is now Belgium and the Netherlands. With the growth of Paris and its suburbs, the population of the Seine department increased tremendously, and by 1968 it contained 5,700,754 residents (45% of them living in the city of Paris, 55% in the suburbs), and was now by far the most populous department of France. It was judged that the Seine department was now too large and ungovernable, and so on January 1, 1968 it was split into four smaller departments: Paris, Hauts-de-Seine, Seine-Saint-Denis, and Val-de-Marne.