Peter (Petter) Jacob Hjelm (2 October 1746 – 7 October 1813) was a Swedish chemist and the first person to isolate the element molybdenum in 1781, four years after its discovery.
After his studies at the University of Uppsala he received his Ph.D. He became professor at the Mining academy and in 1782 he became head of the Royal Mint. From 1784 on he was a member of the Royal Swedish Academy of Sciences. His last position was at the laboratory of the Ministry of Mining.
- Friedrich, Christoph (1989). "Deutsch-schwedische Wissenschaftsbeziehungen an der Universität Greifswald zwischen 1770 und 1850 unter besonderer Berücksichtigung von Chemie und Pharmazie". Berichte zur Wissenschaftsgeschichte. 12 (3): 177–192. doi:10.1002/bewi.19890120307. PMID 11629776.