Pedro Nunes (Portuguese: [ˈpeðɾu ˈnunɨʃ]; Latin: Petrus Nonius; 1502 – 11 August 1578) was a Portuguese mathematician, cosmographer, and professor, probably from a New Christian (of Jewish origin) family.

Considered one of the greatest mathematicians of his time, Nunes is best known for being the first to approach navigation and cartography with mathematical tools. Among other accomplishments, he was the first to propose the idea of a loxodrome (a rhumb line), and was the inventor of several measuring devices, including the nonius (from which the Vernier scale was derived), named after his Latin surname.

Little is known about Nunes' early education, life or family background, only that he was born in Alcácer do Sal in Portugal, his origins are possibly Jewish and that his grandchildren spent a few years behind bars after they were accused by the Portuguese Inquisition of professing and secretly practicing Judaism. He studied at the University of Salamanca, maybe from 1517 until 1522. He returned to Lisbon c. 1529 and started teaching at the University.

He continued his medical studies but held various teaching posts within the University of Lisbon, including Moral, Philosophy, Logic and Metaphysics. He obtained his doctorate in medicine in 1532. When, in 1537, the Portuguese University located in Lisbon returned to Coimbra, he moved to the re-founded University of Coimbra to teach mathematics, a post he held until 1562. This was a new post in the University of Coimbra and it may have been established to provide instruction in the technical requirements for navigation: clearly a topic of great importance in Portugal at this period, when the control of sea trade was the primary source of Portuguese wealth. Mathematics became an independent post in 1544.

In addition to teaching he was appointed Royal Cosmographer in 1529 and Chief Royal Cosmographer in 1547: a post which he held until his death.

In 1531, King John III of Portugal charged Nunes with the education of his younger brothers Luís and Henry. Years later Nunes was also charged with the education of the king's grandson, and future king, Sebastian.

It is possible that, while at the University of Coimbra, future astronomer Christopher Clavius attended Pedro Nunes' classes, and was influenced by his works. Clavius, proponent of the Gregorian Calendar, the greatest figure of the Colégio Romano, the great center of Roman Catholic knowledge of that period, classified Nunes as “supreme mathematical genius". Nunes died in Coimbra.

Pedro Nunes lived in a transition period, during which science was changing from valuing theoretical knowledge (which defined the main role of a scientist/mathematician as commenting on previous authors), to providing experimental data, both as a source of information and as a method of confirming theories. Nunes was, above all, one of the last great commentators, as is shown by his first published work “Tratado da Esfera”, enriched with comments and additions that denote a profound knowledge of the difficult cosmography of the period. He also acknowledged the value of experimentation.