The New York City Police Department (NYPD), which was established in 1845, is currently the largest police force in North America, with primary responsibilities in law enforcement and investigation within the five boroughs of New York City. The NYPD is considered to be one of the first "modern" style police departments in the United States along with the Boston Police Department. The NYPD has a broad array of specialized services, including tactical operations, K-9, harbor patrol, air support, bomb disposal, counter-terrorism, intelligence, anti-gang, narcotics, public transportation, and public housing. NYPD has extensive crime scene investigation and laboratory resources, as well as units which assist with computer crime investigations. The NYPD's headquarters houses an anticrime computer network, essentially a large search engine and data warehouse operated by detectives to assist officers in the field with their investigations. According to the department, its mission is to "enforce the laws, preserve the peace, reduce fear, and provide for a safe environment."

The New York City Transit Police and Housing Police were fully integrated into the NYPD in 1995; Police officers are randomly assigned to the Transit and Housing units upon graduation of the police academy. Members of the NYPD are frequently referred to by the nickname New York's Finest. The NYPD is headquartered at One Police Plaza located on Park Row across the street from City Hall.

The size of the force has fluctuated, depending on crime rates, politics, and available funding. The overall trend, however, shows that the number of sworn officers is decreasing. In June 2004, there were about 40,000 sworn officers plus several thousand support staff; In June 2005, that number dropped to 35,000. As of November 2007, it had increased to slightly over 36,000 with the graduation of several classes from the Police Academy. The NYPD's current authorized uniformed strength is 37,838. There are also an approximate 4,500 Auxiliary Police Officers, 5,000 School Safety Agents, 2,300 Traffic Agents, and 370 Traffic Agent Supervisors.