Carolina (/ˌkæroʊˈliːnə/; Spanish pronunciation: [kaɾoˈlina]) is a city and municipality on the northeastern coastal plain of Puerto Rico, immediately east of San Juan and Trujillo Alto, north of Gurabo and Juncos, and west of Canóvanas and Loíza. Part of the San Juan metropolitan area, Carolina is spread over 12 barrios and the downtown area and administrative center of Carolina Pueblo. In the coastal region of the municipality lies the resort and residential district of Isla Verde, where the main international airport of Puerto Rico, the Luis Muñoz Marín International Airport, is located. Carolina is the third most populated municipality in the archipelago and island.

The town was founded by Spanish colonists in 1816 as Trujillo Bajo ("lower Trujillo"), along with its counterpart Trujillo Alto after Trujillo, Spain. In 1857 it was renamed to San Fernando de la Carolina, later shortened to Carolina, after Charles II of Spain.

The city is known as "Tierra de Gigantes" (Land of Giants), not only for well-known Carolina resident Don Felipe Birriel González (who was 7'11"), but also in honor of other people from Carolina, including poet Julia de Burgos and most notably the first Latin American player named to baseball's Hall of Fame, Roberto Clemente. Carolina was also home to Jesús T. Piñero, the first Puerto Rican to be appointed as governor by the United States government. The city is also known as "El Pueblo de los Tumba Brazos" (The Arm Hackers' Town). During the late 1800s, the town's major export was sugarcane.

Puerto Rico was ceded by Spain in the aftermath of the Spanish–American War under the terms of the Treaty of Paris of 1898 and became a territory of the United States. In 1899, the United States Department of War conducted a census of Puerto Rico finding that the population of Carolina was 11,965.

Hurricane Maria on September 20, 2017 caused flooding in Carolina. The Río Grande de Loíza floods left around 500 homes uninhabitable. The Roberto Clemente stadium lost its roof and many other structures, bridges and roads were damaged to a toll of $87 million. Given the Luis Muñoz Marín International Airport is in Carolina, the destruction in Carolina created a challenge and the airport remained closed for three days. Two weeks after, the airport was attempting to operate a more regular schedule, but electricity was inconsistent and on October 10, nearly a month after the hurricane the airport was running on generators again.

Carolina municipality has a number of rivers such as the Río Canovanillas, Río Grande de Loíza, La Torrecilla, Piñones Lagoons.

Like all municipalities of Puerto Rico, Carolina is subdivided into barrios. The municipal buildings, central square and large Catholic church are located in a small barrio referred to as "el pueblo", near the center of the municipality.

Barrios (which are, in contemporary times, roughly comparable to minor civil divisions) and subbarrios, are further subdivided into smaller areas called sectores (sectors in English). The types of sectores may vary, from normally sector to urbanización to reparto to barriada to residencial, among others.