The duumviri (Latin for "two men"), originally duoviri and also known in English as the duumvirs, were any of various joint magistrates of ancient Rome. Such pairs of magistrates were appointed at various periods of Roman history both in Rome itself and in the colonies and municipia.

Duumviri iuri or iure dicundo were the highest judicial magistrates in the cities of Italy and its provinces. Their chief duties were concerned with the administration of justice. The activities of these individuals are described in the local statutes such as Lex Julia, Lex Irnitana, Lex Malacitana, Lex Rubria, Lex Coloniae, and Genetivae Iuliae. The office was determined by election and lasted one year. They were also expected to deal with public finance of a city, deal with proceedings in the Ordo decurionum, the town council, and run the elections in the comitium or assembly. Combined with the aediles, they formed the quattuorviri, a board of four officials. It was often the case that the emperor was elected as one duumvir and the other position was left up to the emperor for the appointment of a praefectus.