A quaestor (British English: KWEE-stər, American English: , Latin: [ˈkʷae̯stɔr]; "investigator") was a public official in Ancient Rome. There were various types of quaestors, with the title used to describe greatly different offices at different times.

In the Roman Republic, quaestors were elected officials who supervised the state treasury and conducted audits. When assigned to provincial governors, the duties were mainly administrative and logistical, but also could expand to encompass military leadership and command. It was the lowest ranking position in the cursus honorum (course of offices); by the first century BC, one had to have been quaestor to be eligible for any other posts.

In the Roman Empire, the position initially remained as assistants to the magistrates with financial duties in the provinces, but over time, it faded away in the face of the expanding imperial bureaucracy. A position with a similar name (the quaestor sacri palatii) emerged during the Constantinian period with judicial responsibilities.