Val-d'Oise (French: [val dwaz] ⓘ, "Vale of the Oise") is a department in the Île-de-France region, Northern France.

[4] It is named after the river Oise, a major tributary of the Seine, which crosses the region after having started in Belgium and flowed through Northeastern France.

The southernmost region of the department forms part of the Seine Valley and occupies the whole of the small Vallée de Montmorency.

These parts are heavily urbanised, but the ancient Roman road, the Chaussée Jules César, which linked Paris and Rouen, passes through the latter.

The northern, eastern and western parts are fertile areas of agricultural land producing large quantities of corn, sugar beet, and other crops.

The department has a rich archaeological and historical heritage, but is not a region visited much by tourists, perhaps being overshadowed by the French capital.

Places of interest include the following sites;[13] La Roche-Guyon with a castle on top of a rocky hill and a twelfth century château; L'Isle-Adam, a historic small town on the bank of the River Oise; Auvers-sur-Oise, which owes its international fame to its landscapes and the impressionist painters such as Charles-François Daubigny, Paul Cézanne, Jean-Baptiste-Camille Corot, Camille Pissarro and Vincent van Gogh who immortalised them; Enghien-les-Bains, a spa resort with a hot, sulphurous spring, on the site of what was originally Lake Enghien; Écouen with a fine château which houses the Museum of the Renaissance; Cergy-Pontoise, the new administrative capital which has been created out of thirteen communes and has quadrupled in population since the 1960s.

It is in a scenic location by the River Seine and has been much-painted by Claude Monet, Eugène Delacroix, Pierre-Auguste Renoir, Gustave Caillebotte, Alfred Sisley and Georges Braque.