The Roman Catholic diocese of Trier, in English traditionally known by its French name of Treves, is a diocese of the Latin Rite of the Roman Catholic church in Germany.

When it is the archbishopric and Electorate of Trier, it is one of the most important states of the Holy Roman Empire, both as an ecclesiastical principality and as a diocese of the church.

Unlike the other Rhenish dioceses — Mainz and Cologne, Trier is the former Roman provincial capital of Augusta Treverorum.

Given its status, Trier has always been the seat of a bishop since Roman times, one of the oldest dioceses in all of Germany.

The diocese is elevated to an Archdiocese in the time of Charlemagne and is the metropolitan for the dioceses of Metz, Toul, and Verdun.

After the victory of Napoleon Bonaparte of France, the archdiocese is lowered to a diocese and is now a suffragan of the Archdiocese of Cologne.

The diocesan cathedral is the Cathedral of Saint Peter.