Arecibo (/ˌærəˈsiːboʊ/; Spanish pronunciation: [aɾeˈsiβo]) is a city and 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 it is the core city of the Arecibo Metropolitan Statistical Area and part of the greater San Juan–Bayamón, PR Combined Statistical Area. It is spread over 18 barrios and Arecibo Pueblo (the downtown area and the administrative center of the city). Its population in 2020 was 87,754.

The Arecibo Observatory, which housed the Arecibo telescope, the world's largest radio telescope until July 2016, is located in the municipality. The Arecibo telescope collapsed on December 1, 2020. Arecibo is the seat of the Roman Catholic Diocese of Arecibo.

The name Arecibo comes from Arasibo, the Taíno cacique of the yucayeque "settlement" of Abacoa, where the Spanish town of Arecibo was established in 1556. The word Arasibo itself most likely comes from the Taíno words ara, possibly meaning or related to "people", and siba, most likely meaning "rock" or "stone". This name also lends itself to the river which flows through the municipality into the Atlantic Ocean.

Some of the city's nicknames are Villa del Capitán Correa ("Villa of Captain Correa"), after Antonio de los Reyes Correa, a Spanish soldier who famously and successfully defended the city from a British invasion; La Muy Leal ("the very loyal"), after a title often granted to Spanish colonial cities; and Diamante del Norte ("Diamond of the North"), due to the city's location on the northern coast of the island.

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. Arecibo was officially founded as a town by the Spanish crown on May 1, 1616, under the governorship of Captain Felipe de Beaumont y Navarra, when the King of Spain granted the land (and the Taino living there) to Lope Conchillos.

For some time the island was competed for by other European powers. On August 5, 1702, Captain Antonio de los Reyes Correa, commanding 30 militiamen, successfully defended Arecibo from an attack by two Royal Navy warships under William Whetstone. Whetstone's ships landed 40 marines and sailors on two rowboats, but Correa's troops ambushed the invaders, killing 22 and forcing the remainder to retreat. Spanish cannon fire also killed 8 men onboard Whetstone's ships. The Spanish defenders suffered one killed and three wounded, including Correa. This gave the city its nickname "The Village of Captain Correa".

In 1778, Arecibo, by royal decree, was awarded the "Villa" status, though it was not integrated as such until 1802. In 1850 it was awarded the "Muy Leal" (very loyal) title. Over time, large part of its territory became separate municipalities. These include Manati, Barceloneta, Florida, Utuado, Jayuya, Hatillo, Camuy, Quebradillas and Isabela. In 1982, it was promoted to city status, though it continued to be known by its previous nickname.

Hurricane Maria on September 20, 2017, triggered extensive flooding, and damage to infrastructure with over 3,000 people losing their homes. Two hospitals were damaged and the hurricane caused deaths as well.