Petrus comes from the Greek meaning "rock", and is the common English prefix "petro-" used to describe rock-based substances, like petros-oleum or "rock oil." Petrus (Peter) is a common name for people from antiquity through the medieval era, and may refer to one of the following:
- Petrus may refer to Saint Peter, the first pope;
- Petrus Peregrinus, 14th century French scientist;
- Petrus Canisius, 16th century German Catholic theologian and polemicist;
- Petrus Abailardus, Latin name for Abelard;
- Priest Petrus, 5th century Illyrian priest;
- Pietro d'Abano or Petrus de Abano, (1257 – 1315) Italian philosopher and doctor;
- Petrus de Amalfia, 14th century Italian music theorist;
- Petrus de Cruce, late 13th century composer and author, one of the most significant and influential composers of the late ars antiqua;
- Petrus de Picardia, 13th century French music theorist;
- Petrus de Sancto Dionysio, 14th century French music theorist;
- Petrus frater dictus Palma ociosa, 14th century French music theorist, one of the first to illustrate current musical innovations;
- Petrus Le Viser, late 13th century musician, important in the history of tempo and rhythm;
- Petrus optimus notator, 13th century musical scribe in Paris, important for notating Notre Dame polyphony;
- Petrus Trothun Aurelianis, 13th century singer of the Notre Dame School, mentioned in the writings of Anonymous IV.
- Château Pétrus, one of the great wine producers of Pomerol, Bordeaux.
- Petrus Aureolus
- Petrus Baldus de Ubaldis
- Petrus Jacobus Joubert
- Petrus Ramus
- Petrus Alfonsus, Spanish Jewish writer
- Petrus Bernardinus, Florentine sectarian
- Petrus Christus, painter
- Petrus Diaconus, several people
- Petrus de Natalibus, Venetian hagiographer
- Peter of Capua, an Italian scholastic
