Ouest is one of the ten departments of Haiti. It is the jurisdictional seat of the national capital, the city of Port-au-Prince. It has an area of 4,982.56 square kilometers (1,923.78 sq mi) and a population of 4,029,705 (2015 Estimate). It borders the Dominican Republic to the east.

It is the second-largest department in Haiti after the Artibonite. Gonâve Island is also part of the Ouest Department. The department's stretch of coastline lies entirely in the Gulf of Gonâve.

The Department of Ouest is subdivided into five arrondissements, which are further subdivided into twenty communes.

    Arcahaie Arrondissement (180,564)

•  Arcahaie (118,501)
• Cabaret (62,063)

    Croix-des-Bouquets Arrondissement (431,789)

• Cornillon (54,254)
• Croix-des-Bouquets (227,012)
• Fonds-Verettes (45,491)
• Ganthier (56,869)
• Thomazeau (48,163)

    La Gonâve Arrondissement (79,188)

•  Anse-à-Galets (56,890)
•  Pointe-à-Raquette (22,298)

    Léogâne Arrondissement (463,140)

• Grand-Goâve (124,135)
• Léogâne (181,709)
• Petit-Goâve (157,296)

    Port-au-Prince Arrondissement (2,509,939)

• Carrefour (465,019)
• Cité Soleil (241,055)
• Delmas (359,451)
• Gressier (33,152)
• Kenscoff (52,232)
• Pétion-Ville (342,694)
• Tabarre (118,477)
• Port-au-Prince (897,859)