The New York City Police Department was established in May of 1845, which along with the Boston Police Department, was among the first modern police forces in the United States. The NYPD was closely modeled after the Metropolitan Police Service in London, which in turn used a military-like organizational structure, with rank and order. Throughout the years, the NYPD has dealt with a number of riots in New York City, including the 1863 Draft Riots. Early in its history, the NYPD was used as political tool, with positions awarded by politicians to loyalists. Around the turn of the century, the NYPD began to professionalize under leadership of then Police Commissioner, Theodore Roosevelt. The Lexow Committee made some reform recommendations, suggesting a civil service system. The NYPD also began to emphasize training, and took advantage of technological innovations such as fingerprinting.

In recent years, the NYPD has overseen a great reduction in the amount of crime in the city. While there are many theories on why the city's and the nation's crime rate has dropped so substantially many credit the NYPD's CompStat approach. The Compstat program, introduced under then-Commissioner Bill Bratton and Mayor Rudy Giuliani in the 1990s, uses data about crime rates and arrests to evaluate police precincts and commands. COMPSTAT assists the department in understanding where most crimes occur, which allows them to dedicate extra resources to that area. Other observers credit Mayor Giuliani's strategy to encourage the NYPD to crack down on minor "quality of life" crimes such as turnstile jumping, squeegee men, panhandling, etc. He believed that a crackdown on these types of crime would give the police an opportunity to search more suspects, thereby taking guns and drugs off the street and contribute to the public perception that New York City was a lawful environment where crime was not tolerated. Supporters of this approach say that the reduced crime rate shows his approach to be correct, however others point to the nationwide reduction in crime over the same time period as evidence that demographic changes in the United States caused crime rates to drop, not NYPD specific approaches like COMPSTAT.