Petrus Josephus Zoetmulder S.J. (January 29, 1906 – July 8, 1995) was a Dutch expert in the Old Javanese language. He came from Utrecht and was associated with the Society of Jesus by 1925. He worked at Leiden University in the 1930s. His first work appeared in 1930 and he continued to write into the 1990s. He lived in Yogyakarta and was interred in the Jesuit necropolis at Muntilan, Java.
His work was important in the understanding of linguistic studies of Java. He also did works on Monism and Muhammad. Merle Ricklefs translated his thesis in the 1990s.
Zoetmulder was born in Utrecht, Netherlands. From his early childhood, "Piet"—as he was called—was able to read and write even before entering school. His mother Catharina née Noelege was a professional pianist and had been a patient teacher to Piet such that he was able to be admitted to primary school without having to attend kindergarten due to his reading and writing skills. At school he was known to be a conscientious, talented and smart student. His father was an engineer.
Piet was raised in a Roman Catholic family, and while attending the Canisius College Mater Dei gymnasium he became interested in becoming a priest, specifically as a member of the Society of Jesus. Two of his uncles were priests, and an aunt had been a nun in Africa and Suriname. His father had to move to the town of Heerlen for his work as a public health engineer, so Piet attended a gymnasium at Rolduc instead, which was also his father's alma mater. He graduated in the A and B academic tracks. In 1925 he was admitted to the Society of Jesus Novitiate School to begin his training as a priest.