Caloocan, officially the City of Caloocan (Filipino: Lungsod ng Kalookan; IPA: [kalɔˈʔokan]), is a highly urbanized city in Metro Manila, Philippines. According to the 2020 census, it has a population of 1,661,584 people making it the fourth-most populous city in the Philippines.

Caloocan is divided into two geographical locations with a total combined area of 5,333.40 hectares (13,179.1 acres), a result of the 1949 expansion of Quezon City, which absorbed much of its territory. It was formerly part of the Province of Rizal in southern Luzon. It comprises what is known as the CAMANAVA area along with the cities of Malabon, Navotas and Valenzuela.

South Caloocan is bordered by Manila, Quezon City, Malabon, Navotas and Valenzuela. The presence of commercial and industrial activities combined with residential areas make it a highly urbanized central business district and a major urban center in the Northern District of Metropolitan Manila. North Caloocan shares its border with Quezon City and Valenzuela, Marilao, Meycauayan and San Jose del Monte in the province of Bulacan, and Rodriguez in the province of Rizal. It is composed of mostly residential subdivisions and extensive resettlement areas with scattered distribution of industrial estates mostly within road transit points and intersections.

Caloocan as a toponym comes from the Tagalog words lo-ok that translates to "bay", sulok that means "corner" suggested by its location between the ends of the present-day Malabon and Tondo, Manila, and kalook-lookan (or kaloob-looban) meaning "innermost area". The city's name is colloquially spelled Kalookan. Historically, it was called Kaloogan, meaning "interior territory," which evolved from the old Tagalog word "loog" (synonymous with "loob," meaning "inside"). The "g" sound could have shifted to the "k" sound in Tagalog phonetics (e.g. baksak → bagsak), leading to the present name of the city.

There is a mixed preference over the preferred spelling of the city's name. Variation, and the apparent confusion over the spelling, came about during the early 1970s, when a resolution was adopted by the municipal board, requiring the city departments to use the name "Kalookan." However, execution of the resolution was interrupted due to martial law imposed nationwide in September 1972. In 1988, Councilor Aurora Asistio-Henson proposed Resolution No. 006, aiming to promote Filipino nationalism by enforcing the spelling "Kalookan" in all city departments and establishments. Despite this, the change was met with opposition from residents, business owners, and officials. Former representative and mayor Virgilio Robles deemed the move illegal, asserting that the city's name is spelled as "Caloocan" according to the city charter. Although confusion persists, the general inclination in the city is towards "Caloocan," as evidenced by the official logo and favored by many barangays, schools, and newspapers. However, some entities, like the Directories of the Philippines Corporation, prefer the spelling "Kalookan."

Originally, Caloocan was the area where the old town of Tondo and Tambobong met, located along the shores of Dagat-Dagatan, a crescent-shaped inland lagoon to the west. The settlement along the shore was called "Aromahan", or "Espina" to the Spaniards, and was separated from Manila Bay by a narrow ridge from Tondo towards an opening in Kinabutasan leading to the sea.

By the late 1700s, the fishermen of Aromahan have expanded towards a hill east of Dagat-Dagatan. This naturally stony hill was called "Kaloogan", meaning "interior territory." With Aromahan relegated to the periphery, this hilltop area was also settled by oppressed people from Tondo, becoming the new center of the community by 1802. To the east was a vast stretch of cogon-covered land. Eventually called "Kalaanan", meaning flat grassland in old Tagalog, this area is now generally known as Grace Park.

Caloocan became a municipality when it was separated from Tondo in 1815. Its original territory extended to the foothills of Marikina, San Mateo and Montalban to the east; Tinajeros, Tanza, and Tala rivers to the north; San Juan del Monte, San Francisco del Monte, Sampalok, Santa Cruz and Tondo in the south; and Dagat-dagatan and Aromahan to the west. The local government building was set up on the relatively well-settled portion just above Libis Espina. The old Aromahan chapel was finally abandoned and a new church was built facing the municipal hall. To escape the Spanish authorities, many from the area abandoned the town proper and sought refuge in the grasslands of Balintawak and Pugad-Lawin, in which the people fought the landlords of Hacienda de Maysilo for terrestrial rights, which went on for almost a hundred years.

Caloocan is historically significant because it was the center of activities for the Katipunan, the secret militant society that launched the Philippine Revolution during the Spanish occupation of the Philippines. In a house in Caloocan, secret meetings were held by Andrés Bonifacio and his men, and it was in the city's perimeters where the first armed encounter took place between the Katipunan and the Spaniards. The revolution erupted after the "Cry of Balintawak" led by Andres Bonifacio against their oppressors on August 30, 1896.

In 1899, the people of Caloocan showed resistance to coming to terms with the Americans, who were bent on extending their supremacy over the country. The men of Caloocan fought the new invaders on February 23, 1899, however victory eluded the local troops on the pretext of Antonio Luna's rift with Emilio Aguinaldo's loyalists. The city then saw heavy fighting in the Philippine–American War, at the Battle of Caloocan and the Second Battle of Caloocan.

In 1901, under the American regime, Caloocan, previously a part of the province of Manila, became one of the municipalities of the newly established province of Rizal. Due to the consolidation of several municipalities in 1903, Novaliches, then an independent municipality, became part of Caloocan pursuant to Act No. 942, as amended by Act Nos. 984 and 1008 of the Philippine Commission.

In 1942, Caloocan was one of the municipalities of Rizal merged alongside Manila and Quezon City to form the City of Greater Manila as an emergency measure by President Manuel L. Quezon. It regained its pre-war status as a municipality of Rizal when the City of Greater Manila was dissolved effective August 1, 1945.

In 1961, after Republic Act No. 3278 was approved by the Philippine Congress, a plebiscite was conducted. Caloocan was officially inducted into cityhood on February 16, 1962.

Caloocan remained a city of the province of Rizal until November 7, 1975, when it became a part of the National Capital Region or Metro Manila, by virtue of Presidential Decree No. 824.

Caloocan once encompassed a much larger, contiguous area. The districts of Balintawak, La Loma and Novaliches were once part of Caloocan. Balintawak is a historic district because it was the original site of the "Cry of Pugad Lawin" (Unang Sigaw sa Balintawak) at a location called "Kang-kong" near Tandang Sora's house. Novaliches was an expansive sector with some hillsides that served as meeting places and hideouts for Andrés Bonifacio and the Katipunan.

During the American occupation, there was a consolidation of several municipalities. Caloocan annexed the neighboring town of Novaliches on October 12, 1903, as stated in the Act No. 942 of the Philippine Commission, bringing its total area to about 1,500 hectares (3,700 acres). When Commonwealth Act No. 502 created Quezon City in 1939, Caloocan ceded 1,500 hectares of land from the barrios or sitios of Bagubantay (Bago Bantay), Balintauac (Balintawák), Balingasa, Kaingin, Kangkong (present-day Apolonio Samson), La Loma, Malamig, Matalahib (present-day Santo Domingo), Masambong, Galas, San Isidro, San José, Santol and Tatalon. Instead of opposing the transfer, Caloocan residents willingly gave the land in the belief it will benefit the country's new capital city.

However, in 1949, Congress passed Republic Act No. 392, which redefined the Caloocan–Quezon City boundary. The barrios of Baesa, Sangandaan, Talipapâ, San Bartolomé, Pasong Tamó, Novaliches Proper (poblacion), Banlat (present-day Tandang Sora), Kabuyao, Pugad Lawin, Bagbag, Pasong Putik, which once belonged to Novaliches and had an area of about 8,100 hectares (20,000 acres), were excised from Caloocan. The remaining portion of the Novaliches is now called North Caloocan. This split Caloocan into two parts: a more urbanized southern section and a suburban-rural northern section, which is part of Novaliches.

In 1957, the sitio of Bagbaguin was separated from the barrio of Caybiga (Kaybiga) and converted into a distinct barrio known as Barrio Bagbaguin.

Issues concerning budget and handling village governments led to attempts to restructure the city's barangays since late 1980s. A bill authored by city's 1st district representative Virgilio Robles, which aimed to reduce the barangays from 188 to 60—thirty in each legislative district—was approved as Republic Act (RA) No. 6714 on February 28, 1989. A plebiscite was held on March 10; with a turnout of only 10% of 384,981 registered voters, majority of the participated voters reportedly opposed the proposal.

On the other hand, residents of Bagong Silang (Barangay 176), then the country's most populous barangay and was used to be a relocation site for informal settlers, appealed the partition of the barangay since 2013. On April 3, 2024, President Bongbong Marcos signed RA No. 11993 which would divide the village into six. This was ratified by the majority of voters in a plebiscite held on August 31.

Throughout Oscar Malapitan's mayorship from 2013 to 2022, he regularly boasted of a decreased crime rate in Caloocan. However, the Peace Research Institute Frankfurt (PRIF) noted in 2020 that Malapitan's mayorship was characterized with a passivity towards President Rodrigo Duterte's war on drugs during its first year (2016–2017), with Malapitan asking the local branch of the Philippine National Police (PNP) to take charge of crime control and work vigorously against illegal drugs, which PRIF claimed to have "resulted in a huge spike of deadly police violence" and "excessive levels of vigilantism" during this period. Many of the high-profile incidents in Duterte's national drug war occurred in Caloocan, including the murders of Luis Bonifacio and his son Gabriel in 2016 and the murders of Kian delos Santos, Carl Arnaiz and Reynaldo de Guzman in 2017.

Bishop Pablo Virgilio David of the Diocese of Kalookan met with Malapitan, lawyer Sikini Labastilla, and the city police chief, all three of whom were members of the Caloocan City Anti-Drug Abuse Council (CADAC), sometime in 2017 to discuss how to better facilitate rehabilitation and drug prevention in the city during the drug war, which lead to the establishment of the Caloocan Anti-Drug Abuse Office (CADAO) in early September through an ordinance written by councilor Rose Mercado. Caloocan also passed Ordinance No. 702, sponsored by councilors Mercado, Onet Henson and Alou Nubla, in early September that implemented a new curfew for minors (from 10 p.m. to 5 a.m.) and placed the liability on their parents in response to the police murders of delos Santos, Arnaiz and de Guzman. By mid-September, Caloocan's entire police force was relieved from duty by PNP Chief Oscar Albayalde, despite it receiving the award for Metro Manila's Best City Police Station from the National Capital Region Police Office (NCRPO) a month earlier; only newly assigned police chief Jemar Modequillo and his administration deputy were retained. Although Modequillo attempted to instill discipline in the city's police force and reduce the number of deaths in police operations in the months after his assignment, he was characterized by his support for Duterte's drug war and observance of his mandate.

In March 2018, a spate of drive-by shootings perpetrated by pairs of motorcyclists, locally known as "riding-in-tandem", occurred in the city. By next month, councilors Mercado, Nubla and PJ Malonzo proposed an ordinance that would ban motorcycle-riding male tandems, but upon the protest of motorcycle clubs, however, mayor Malapitan stated that changes will first be made to the proposed ordinance before he signs it into law.

Caloocan is divided into two non-contiguous areas with a total combined area of 53.334 square kilometers (20.592 sq mi). South Caloocan, with an area of 13.625 square kilometers (5.261 sq mi), is bordered on the south by Manila, on the east by Quezon City, on the west by Navotas, on the north-northwest by Malabon, and on the north by Valenzuela. North Caloocan, with an area of 39.709 square kilometers (15.332 sq mi), shares its border on the south-southeast by Quezon City, on the southwest by Valenzuela, on the north by Marilao, Meycauayan and San Jose del Monte in the province of Bulacan, and on the northeast by Rodriguez in the province of Rizal.

South Caloocan, where most commercial and industrial establishments are found, lies on generally flat and highly accessible land, with slopes ranging from 0–3%. The topography gradually changes from gently to moderately sloping to rolling along the North Luzon Expressway, with slopes ranging from 3–18%. The highest point at 35.00 meters (114.83 ft) above sea level can be found in this area, while the lowest point is in the southern part of Dagat-Dagatan at about 0.993 meters (3 ft 3.1 in) above mean sea level.

North Caloocan is characterized by gently to steeply undulating to rolling topography with slopes ranging from 3–18%, mostly seen in the northern and central portion, gradually transforming into a southward trend of flat lands down to the southwestern tip of the boundary. Being accessible to major roads, many industrial and residential subdivisions have been developed on this near-level land.

The geologic formation of the two portions of Caloocan varies in type and characteristics. and are specifically classified as quaternary alluvium, tuff and tuffaceous sediment, pyroclastic flow deposit, and conglomerates. The formation on the eastern half of Metropolitan Manila extending to the coastline of Manila Bay and including a greater part of South Caloocan is the quaternary alluvium, which consists of unconsolidated stream-deposited sediments that include sand, silt, clay and gravel.

Eastward of South Caloocan, large areas consisting of tuff and tuffaceous sediment can be traced, spreading towards the whole eastern side of Metro Manila. Pyroclastic flow deposit or igneous rocks formed by the lithification of ash flow are likewise present in some northern fringes of South Caloocan and in most parts of North Caloocan. On the northeast borders of North Caloocan, conglomerate rocks were traced, crossing Tala Estate and extending to the province of Bulacan and the La Mesa Watershed.

Soil found in both areas of Caloocan predominantly falls under the Novaliches Series, covering 96% of the total land area of the city. The Novaliches Series is composed of reddish brown soil, friable in consistency and granular in structure. Spherical concretions are present in the subsoil and underneath is tuffaceous material of varying degrees of disintegration and weathering. This tuffaceous material is exposed by extensive erosion in some places.

Caloocan has surface waters that either have natural courses (creeks and rivers) or were constructed to serve as drainages to remove excess water from soil surfaces. South Caloocan has about 5.0-kilometer-long (3.1 mi) open drainage canals that serve mainly the reclamation area comprising Kaunlaran Village (Dagat-Dagatan Development Project) and nearly 11.3-kilometer-long (7.0 mi) natural surface water coursing through the different natural river systems. These include the Tinajeros-Tullahan River along the Caloocan–Valenzuela boundary; Maligaya Creek within La Loma Cemetery and crossing Rizal Avenue Extension; Casili Creek which terminates in Estero de Maypajo, and Cantarilla/Panaca Creek along the Caloocan–Malabon boundary. In North Caloocan, all surface waters consist of natural streams, the longest being the Meycauayan-Marilao River dividing Caloocan and Bulacan. Others include the Bagong Silang River, Tala, Camarin, Pasong Malapad, and Bagumbong Creeks crossing multiple subdivisions, for 52.7 kilometers (32.7 mi) long within the city's territorial boundaries.