Pehr Kalm (6 March 1716 – 16 November 1779) (in Finland also known as Pietari Kalm and in some English-language translations as Peter Kalm) was a Swedish-Finnish explorer, botanist, naturalist, and agricultural economist. He was one of the most important apostles of Carl Linnaeus.
In 1747 he was commissioned by the Royal Swedish Academy of Sciences to travel to the North American colonies and to bring back seeds and plants that might be useful to agriculture. Among his many scientific accomplishments, Kalm can be credited with the description of Niagara Falls written by a trained scientist; he described this phenomenon along the border of New York (United States) and Canada. In addition, he published the first scientific paper on the North American, 17-year periodical cicada, Magicicada septendecim.
Kalm wrote an account of his travels that was translated into numerous European languages; a 20th-century translation remains in print in English as Peter Kalm's Travels in North America: The English Version of 1770, translated by Swedish-American scholar Adolph B. Benson.
Kalm was born in Ångermanland, Sweden, where his parents had taken refuge from Finland during the Great Northern War. His father died six weeks after his birth. When the hostilities were over, his widowed mother returned with him to Närpes in Ostrobothnia, where Kalm's father had been a Lutheran minister.
Kalm studied at the Academy of Åbo from 1735. In 1740 he entered the University of Uppsala, where he became one of the first students of the renowned naturalist Carolus Linnaeus. In Uppsala, Kalm became the superintendent of an experimental plantation owned by his patron, Baron Sten Karl Bielke.
Kalm did field research in Sweden, Russia, and Ukraine from 1742 to 1746, when he was appointed Docent of Natural History and Economics at the Academy of Turku. In 1747 the Academy elevated him to Professor of Economics. That same year he was also appointed by Linnaeus and the Royal Swedish Academy of Sciences (which he had been a member of since 1745) to travel to North America to find seeds and plants that might prove useful for agriculture or industry. In particular, they wanted him to bring back the red mulberry in the hope of starting a silk industry in Finland (which was then an integral part of Sweden, today also known as Sweden-Finland).
On his journey from Sweden to Philadelphia, Pennsylvania, Kalm spent six months in England, where he met many of the important botanists of the day. Kalm arrived in Pennsylvania in 1748; there he was befriended by Benjamin Franklin and naturalist John Bartram. Kalm based his explorations at the Swedish-Finnish community of Raccoon (now Swedesboro) in southern New Jersey. This town had been founded as part of the former Swedish colony of New Sweden. There he also served as the substitute pastor of Trinity Church, the local Swedish Lutheran church. Kalm subsequently married the widow of Johan Sandin, the former pastor who had died. He remained in Raccoon until 19 May 1749.
Kalm made trips as far west as Niagara Falls and as far north as Montreal and Quebec before returning to Finland in 1751. He took a post as professor at the Turku Academy. In addition to teaching and directing students, he established botanical gardens in Turku. He taught at the Academy until his death in 1771. 
Sweden and Finland had tangled histories, and often both laid claim to prominent people of the region. Kalm's ethnicity and mother tongue were a subject of discussion almost a century after his death, during Finland's so-called language strife. Kalm usually signed letters as "Pehr Kalm," in the Swedish style. He was raised in Närpes, which was then bi-cultural and bi-lingual Finland-Swedish. All his known professional writings were done in Latin and Swedish, then more widely used (especially Latin) than Finnish for scientific works. Anders Chydenius, another noted Swedish scientist from territories that later were part of Finland, was a student of Pehr Kalm's.
- Kalm's journal of his travels was published as En Resa til Norra America (Stockholm, 1753–1761). It was translated into German, Dutch, and French, and into English in 1770 as Travels into North America. Kalm described not only the flora and fauna of the New World, but the lives of the Native Americans and the British and French colonists whom he met.
A United States edition was later translated and edited by Swedish-American scholar and literary historian Adolph B. Benson (1881–1961). It was published as Peter Kalm's Travels in North America: The English Version of 1770 (Wilson-Erickson Inc., 1937). This version has become an important standard reference regarding life in colonial North America and has been in continuous print in several updated editions.
- Kalm's paper on the life cycle of the North American 17-year periodical cicada, Magicicada septendecim, was the first published scientific description of the species and its recurrent appearances.
- In his Species Plantarum, Linnaeus cites Kalm for 90 species, 60 of them new, including the genus Kalmia, which Linnaeus named after Kalm. Kalmia latifolia (Mountain-laurel) is the state flower of Pennsylvania and Connecticut.
- The Mint of Finland issued a coin in Kalm's honor.
- TIEDE 5/2003, Suomalaisten löytöretket 3: Professori Kalm pääsi amerikan lehtiin.
- "Peter Kalm writes to Benjamin Franklin in 1750" (Niagara Falls)
- American Journeys (Wisconsin Historical Society)
- Peter Kalm (Trinity Church - Swedesboro, New Jersey)
- Peter Kalm (L’Encyclopédie de l’histoire du Québec)
- Quebec City in 1749 (ProvinceQuebec.com)
- En Resa til Norra America (Antiquarian Booksellers' Association of America)
- (1) Davis, J.J. (May 1953). "Pehr Kalm's Description of the Periodical Cicada, Magicicada septendecim L., from Kongl. Svenska Vetenskap Academiens Handlinger, 17:101-116, 1756, translated by Larson, Esther Louise (Mrs. K.E. Doak)". The Ohio Journal of Science 53: 139–140. Archived from the original on 2012-10-02. Republished by Knowledge Bank: The Ohio State University Libraries and Office of the Chief Information Officer. Retrieved 2012-10-02.
2) Marlett, C.L. (1898). "The Periodical Cicada in Literature". The Periodical Cicada: An Account of Cicada Septendecim, Its Natural Enemies and the Means of Preventing its Injury, Together With A Summary of the Distribution of the Different Broods (Bulletin No. 14 - New Series, U.S. Department of Agriculture, Division of Entomology). Washington, D.C.: United States Government Printing Office. pp. 112–118.
- Mint of Finland Issues Pehr Kalm Coin, Coin Update News
- "Author Query for 'Kalm'". International Plant Names Index.
- Benson, Adolph B. Peter Kalm's Travels in North America: The English Version of 1770 (v. 1 & 2) (Dover Publishing. 1987) ISBN 978-0-486-25423-4
- Robbins, Paula Ivaska The Travels of Peter Kalm: Finnish-Swedish Naturalist Through Colonial North America, 1748-1751(Purple Mountain Press; 2007) ISBN 978-1-930098-80-0
- Biography, Dictionary of Canadian Biography Online
- "Kalm, Peter". Appletons' Cyclopædia of American Biography. 1892.
- Doria Repository — Theses written or supervised by Pehr Kalm at the Royal Academy of Turku
- Mint of Finland Issues Pehr Kalm Coin, Coin Update News