Peter Matthiessen (born May 22, 1927, New York, New York, U.S.—died April 5, 2014, Sagaponack) was an American novelist, naturalist, and wilderness writer whose work dealt with the destructive effects of encroaching technology on preindustrial cultures and the natural environment. Both his fiction and nonfiction works combined remote settings, lyrical description, and passionate advocacy for the preservation of the natural world.

After serving in the U.S. Navy (1945–47), Matthiessen attended the Sorbonne and Yale University (B.A., 1950). He moved to Paris, where he associated with other expatriate American writers such as William Styron, James Baldwin, and Irwin Shaw. While there he helped found and edit the literary journal The Paris Review with childhood friend George Plimpton in 1953. Matthiessen later admitted that he had formed the magazine at the behest of the Central Intelligence Agency, having been recruited following his college graduation. The agency had felt that he needed more cover for his spying activities, which included reporting on communist developments. He severed his relationship with the agency shortly after the foundation of the magazine.

A dedicated naturalist, Matthiessen embarked on a tour of every wildlife refuge in the United States during the mid-1950s. He wrote more than 15 books of nonfiction, including Wildlife in America (1959), a history of the destruction of wildlife in North America; The Cloud Forest: A Chronicle of the South American Wilderness (1961); and Under the Mountain Wall: A Chronicle of Two Seasons in the Stone Age (1962), about his experiences as a member of a scientific expedition to New Guinea. Blue Meridian: The Search for the Great White Shark (1971) sheds light on a predator about which little is known. The Snow Leopard (1978), set in remote regions of Nepal, won both the National Book Award for nonfiction and the American Book Award.

Matthiessen continued to range far and wide, producing African Silences (1991), Indian Country (1992), and Baikal: Sacred Sea of Siberia (1992). His book In the Spirit of Crazy Horse (1983), about the conflict between federal agents and the American Indian Movement at Wounded Knee, South Dakota, in 1973, was the subject of a prolonged libel suit that blocked all but an initial printing and was not settled until 1990; in 1991 the book was republished. Matthiessen again made impassioned calls for the protection of wildlife in The Birds of Heaven (2001), which details a journey across multiple continents in search of cranes, and Tigers in the Snow (2002), which chronicles the plight of the Siberian tiger. The Peter Matthiessen Reader: Nonfiction 1959–1991 was published in 2000.

Matthiessen’s first novel, Race Rock (1954), follows the exploits and moral degeneration of four young New Englanders. The acclaimed At Play in the Fields of the Lord (1965; film 1991) investigates the cataclysmic convergence of the lives of missionaries, mercenaries, and an isolated tribe of Indians modeled on the Yanomami. Far Tortuga (1975) concerns the events leading up to the death of the crew of a turtle-fishing boat in the Caribbean. A trilogy, composed of Killing Mister Watson (1990), Lost Man’s River (1997), and Bone by Bone (1999), fictionalizes the life of a murderous planter in the Florida Everglades at the beginning of the 20th century. Matthiessen later revised and compiled the three volumes into a single novel, Shadow Country (2008), which won the National Book Award for fiction. In Paradise (2014) details the reflections of a Holocaust scholar on a meditative retreat at Auschwitz.