Arecibo (Spanish pronunciation: [aɾeˈsiβo]) is a municipality on the northern coast of Puerto Rico, on the shores of the Atlantic Ocean, located north of Utuado and Ciales; east of Hatillo; and west of Barceloneta and Florida. It is about 50 miles (80 km) west of San Juan, the capital city. Arecibo is the largest municipality in Puerto Rico by area, and is part of the San Juan, Caguas and Guaynabo Metropolitan Statistical Area. It is spread over 18 barrios and Arecibo Pueblo (the downtown area and the administrative center of the city). Its population in 2010 was 96,440.
The Arecibo Observatory, which housed the Arecibo telescope that was the world's largest radio telescope until July 2016, is located here. The Arecibo telescope collapsed on 1 December 2020. Arecibo is the seat of the Roman Catholic Diocese of Arecibo.
When the Spanish arrived, they found the area occupied by the indigenous Taíno, led by Xamaica Arasibo, Cacique (chief) of the yucayeque (town) then named Abacoa.
Spanish colonists settled Arecibo in 1556, which they named for the cacique. It was their fourth settlement on the island, after Caparra (which later became San Juan), San German, and Coamo.