The United States police-rank model is generally quasi-military in structure.^[1][2] A uniform system of insignia based on that of the US Army and Marine Corps is used to help identify an officer's seniority.^[2][3]

Although the large and varied number of federal, state, and local police and sheriff's departments have different ranks, a general model, from highest to lowest rank, would be:

• Chief of police/commissioner of police/superintendent/sheriff: The title commissioner of police is used mainly by large metropolitan departments, while chief of police is associated with small and medium-sized municipalities; both are typically appointed by a mayor or selected by the city council or commission. In some cities, a "commissioner" is a member of the board of officials in charge of the department, while a "chief" is the top uniformed officer answering to the commissioner or commission. In very large departments, such as the New York City Police Department, there may be several non-police officer deputies and assistant commissioners, some of whom outrank the chief of department and others on par with the uniformed chief. There may be a chief of operations who is second in command to the top-ranking chief. In contrast, sheriffs in the United States are usually elected officials, one in each county, who head the sheriff's department (or sheriff's office).^{[citation needed]}
• Assistant chief of police/Undersheriff/assistant commissioner/assistant superintendent: Only seen in some departments. In New York City, assistant chiefs head borough commands.^{[citation needed]}
• Deputy chief of police/deputy commissioner/deputy superintendent/chief deputy/Assistant Sheriff: The top subordinate of the chief of police, commissioner, superintendent, or sheriff; may or may not have a specific area of responsibility. In some places the undersheriff is the warden of the county jail. The New York City Sheriff's Office has five undersheriffs: each one is responsible for a borough of New York City, with the Sheriff of the City of New York overseeing all of them. In some Sheriff's Offices, the rank of Assistant Sheriff exists, below the Undersheriff, but still above Commander and other ranks.^{[citation needed]}
• Inspector/commander:^[4] Sometimes have an insignia of a single star, analogous to brigadier generals, but in other areas wear a gold or silver eagle, similar to a colonel. "Inspector" is also used as a term for "detective" in the San Francisco Police Department but is two ranks above captain in the NYPD and the Philadelphia Police Department. In the NYPD, inspectors command divisions, which may be groups of precincts within a borough or specialized branches of the police service.^{[citation needed]}
• Colonel or lieutenant colonel: A majority of state police as well as some municipal agencies use "colonel" or "lieutenant colonel" as their senior executive rank, often jointly with a civilian title such as "superintendent, deputy superintendent", "commissioner, deputy commissioner" or "director, deputy director", "Chief, Deputy Chief", etc. Conversely, the colonel or lieutenant colonel rank is rarely employed by other agencies, though it is used by the Baltimore Police Department and other Maryland agencies as either an executive or commander-like rank. Colonels generally wear the gold or silver eagle of a military colonel, and lieutenant colonels have the oak leaf of a Military lieutenant colonel, from the U.S. armed forces. Many sheriffs also wear the eagle insignia, and use colonel as an official rank.^{[citation needed]}
• Major^[5]/deputy inspector: Sometimes Majors/Deputy Inspectors have the insignia of a gold or silver oak leaf, similar to a major or lieutenant colonel in the armed forces. In the Baltimore Police Department and Atlanta Police Department, majors supervise police stations.
• Captain: Two gold or silver bars ("railroad tracks"). A Captain often supervises a police station but can supervise another division or unit (detectives, patrol, etc.) in smaller departments and only certain sections of a police station in larger departments. In the NYPD, captains are the normal commanders of precincts.^{[citation needed]}
• Lieutenant: Wearing a single gold or silver bar, a lieutenant supervises two to three or more sergeants. Lieutenants can supervise an entire watch shift in a police station or detective squad (narcotics, homicide, etc.) in larger police departments, entire barracks in state police departments, and entire precincts in smaller police departments.^{[citation needed]}
• Sergeant: Three chevrons, a police officer who supervises an entire watch shift in smaller departments and areas of a precinct and individual detective squads in larger departments. Some agencies, such as the New Jersey State Police, use a para-militaristic range of sergeant ranks, such as staff sergeant and sergeant first class, in addition to the basic sergeant rank.^{[citation needed]}
• Detective/inspector/investigator: An inspector/detective/investigator usually works in plain clothes. This may be in several classes that correspond to higher supervisory and pay grades. In the NYPD, the detective rank is technically a designation: detectives do not actually outrank police officers although they are in charge of cases and are often senior in years of service, and so have a certain degree of authority beyond police officers in specific situations. Detectives also perform undercover duties for some of their cases.^{[citation needed]}
• Officer/deputy/trooper/corporal: A regular officer or deputy wears no rank insignia, and there may be several pay grades. Corporals, who may be senior officers or acting watch commanders, wear two chevrons. A police corporal is generally employed as an officer as an entry level supervisor position. These duties may include one or more of the following roles:^[6]
  • Detective
  • Division supervisor
  • Field training officer (FTO) (in some departments, field training officers are not given any supervisory powers and hold no higher rank than other officers).^{[citation needed]}

Police corporals will often act as a lead officer in field situations when a sergeant is not present.^[7] The position is also referred to by some agencies as Agent.^[8]

In a few departments, such as New York City, Washington DC, and Baltimore, officers from the rank of lieutenant and up wear white shirts instead of the dark blue or black uniform shirts common to lower-ranked police officers. In Philadelphia the rank of sergeant and up wear white shirts.^[9] Command staff and ranking officers/supervisors may wear fretting ("scrambled eggs") on their hat visors.

Advancement from officer to captain is generally by appointment after successful completion of a series of examinations, and after the officer has sufficient time in grade. Grades above captain are generally by appointment of the chief or sheriff. In addition, there must be vacancies for a higher rank. In police departments, the second-highest rank is usually similar to a chief of staff. In a sheriff's office, the second-highest ranking person is often responsible for most operations, similar to a chief of police in a police department, because the Sheriff is often elected and in many cases is a politician rather than an experienced law enforcement officer.^{[citation needed]}