In the United States, a district attorney (DA), county attorney, county prosecutor, state attorney, state's attorney, prosecuting attorney, commonwealth's attorney, or solicitor is the chief prosecutor or chief law enforcement officer representing a U.S. state in a local government area, typically a county or a group of counties. The exact scope of the office varies by state. Generally, the prosecutor is said to represent the people of the jurisdiction in the state's courts, typically in criminal matters, against defendants. District attorneys are elected in almost all states, and the role is generally partisan. This is unlike similar roles in other common law jurisdictions, where chief prosecutors are appointed based on merit and expected to be politically independent.

The prosecution is the legal party responsible for presenting the case against an individual suspected of breaking the state's criminal law, initiating and directing further criminal investigations, guiding and recommending the sentencing of offenders, and are the only attorneys allowed to participate in grand jury proceedings. The prosecutors decide what criminal charges to bring, and when and where a person will answer to those charges. In carrying out their duties, prosecutors have the authority to investigate persons, grant immunity to witnesses and accused criminals, and plea bargain with defendants.

A district attorney or state attorney leads an office of other prosecutors and related staff. Staff attorneys are most commonly known as assistant district attorneys (ADAs) or deputy district attorneys (DDAs); in states where the head of office is called state attorney the staff attorneys are usually referred to as Assistant State Attorney (ASAs) Most prosecutions will be delegated to the assistant attorneys, with the head-of-office sometimes prosecuting the most important cases and having overall responsibility for the agency and its work. Most criminal matters in the United States are handled in state judicial systems, but a comparable office for the United States Federal government is the United States Attorney.

In most states, DAs are directly elected. They are appointed in Alaska, Connecticut, and New Jersey. In the District of Columbia, the appointed United States Attorney is responsible for prosecuting most offenses under the DC Code, in addition to prosecuting federal offenses.

This term for a prosecutor originates with the traditional use of the term "district" for multi-county prosecutorial jurisdictions in several U.S. states. For example, New York appointed prosecutors to multi-county districts prior to 1813. Even after those states broke up such districts and started appointing or electing prosecutors for individual counties, they continued to use the title "district attorney" for the most senior prosecutor in a county rather than switch to "county attorney".

The principal duties of the district attorney are usually mandated by law and include representing the State in all criminal trials for crimes which occurred in the district attorney's geographical jurisdiction. The geographical jurisdiction of a district attorney may be delineated by the boundaries of a county, judicial circuit, or judicial district.

Their duties generally include charging crimes through informations or grand jury indictments. After levying criminal charges, the state's attorney will then prosecute those charged with a crime. This includes conducting discovery, plea bargaining, and trial.

In some jurisdictions, the district attorney may act as chief counsel for city police, county police, state police and all state law enforcement agencies within the state's attorney's jurisdiction.