Alcobaça (Portuguese pronunciation: [ɐɫkuˈβasɐ]) is a city in Alcobaça Municipality in Oeste Subregion and Leiria District, in Portugal, formerly included in the Estremadura Province. The city grew along the valleys of the rivers Alcoa and Baça, from which it derives its name. The municipality has a total population of 55,269 inhabitants and a total area of 408.1 km². The city itself has a population of 15,800 inhabitants.

The city of Alcobaça became notable after the first king of Portugal, Afonso Henriques, decided to build there a church to celebrate the conquest of Santarém to the Moors, in 1147. The church later evolved into the Monastery of Alcobaça, one of the most magnificent gothic monuments in the country. In the church are the tombs of King Peter I and his murdered mistress Inês de Castro. Over the centuries this monastery had an important role on Portuguese culture.

A few kilometers to the north of Alcobaça is located the Monastery of Batalha, another wondrous gothic building constructed in memory of a different important battle, that of Aljubarrota. To the west of Alcobaça is the well-known former fishing village of Nazaré,now a town. To the south is the city of Caldas da Rainha and the quaint medieval town of Óbidos that is an attraction for any tourists that enjoys a true glimpse of the past. Also to the northeast is the town of Porto de Mós with its fanciful rebuilt castle.