Caguas (Spanish pronunciation: [ˈkaɣwas], locally [ˈkawaʔ]) is a city and municipality in central eastern Puerto Rico. Located in the eponymous Caguas Valley between the Sierra de Cayey and Sierra de Luquillo of the Central Mountain Range, it is bordered by San Juan and Trujillo Alto to the north, Gurabo and San Lorenzo to the west, Aguas Buenas, Cidra and Cayey to the east, and Patillas to the south. With a population of 127,244 as of the 2020 census, Caguas is the fifth most populated municipality in the archipelago and island and a principal city of the San Juan metropolitan area.

Since 2009, Caguas is the only municipality in Puerto Rico recognized as a Tree City USA by the Arbor Day Foundation.

Caguas, originally founded as San Sebastián del Piñal de Caguax, is named after the local Taino chieftain Caguax, who at the time of the Spanish arrival in 1493 was cacique of the yucayeque and region of Turabo. The name Caguax itself might be related to the Taino word for snail or slug: ‘cagua’, similar to other Arawakan and Cariban proper names such as Cagua in Venezuela (from the Cumanagoto word cahigua).

Caguas is nicknamed "Valley of the Turabo" (Valle del Turabo) in reference to the former cacicazgo and yucayeque led by Caguax. The Turabo River is also named after this geopolitical toponym. Other nicknames for Caguas include “the Criollo city” (La Ciudad Criolla) and “the Cradle of Trovadores” (La Cuna de los Trovadores). The city is often known as the “center and heart of Puerto Rico” (Centro y corazón de Puerto Rico) for its geographical location, and one of its municipal anthems bears the same. In recent years the municipality has also been referred to as “the new Caguas country” or “the new land of Caguas” (El nuevo país de Caguas) by the media and the former mayor William Miranda Marín.

As with the rest of Puerto Rico, the Taínos were the primary group living in the valley at the time of the Spanish arrival. The Spanish conquistadors further developed the agriculture in the valley, while also establishing mines in search of gold, silver and copper. Most of the native Taínos living in the area were either forced out or taken as slaves and moved to the Real Hacienda del Toa (in modern-day Toa Alta and Toa Baja). Most of the valley was later cleared of its original vegetation for the development of cattle farms such as Hato de Bairoa, Hato de Caguax and Hato de Gurabo.

Caguas was officially founded on January 1, 1775, as San Sebastián del Piñal de Caguax, with the name later being shortened and modernized to its current form. The site of downtown Caguas and its central square dates to 1779. In 1820, the settlement was granted the title of Villa and it was granted city rights in 1894. Sugarcane was the primary crop during this time and important sugarcane plantations and refineries were those of Central Santa Juana (close to modern day Plaza Centro) and Central Santa Catalina (modern day Las Catalinas Mall). The Carretera Central, which is the first paved road to cross Puerto Rico from north to south connecting San Juan to Ponce, was built during the last two decades of the 19th century, made Caguas more accessible therefore causing the population of the town to grow even more.

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 Caguas was 19,857.

The city grew considerably in size during the 1970s and quickly became an exurb of San Juan to the north due to its location. The region of Caguas became an important pharmaceuticals manufacturing center during this time. Pharmaceutical companies originally came to Puerto Rico in the late 1960s and 1970s to take advantage of the now-expired federal tax incentive known as Section 936. This incentive allowed U.S.-based manufacturers to send all profits from local plants to stateside parent plants without having to pay any federal taxes.