Howard Clinton Zahniser (February 25, 1906 – May 5, 1964) was an American environmental activist. From 1945 until his death he led The Wilderness Society as executive secretary, executive director, and editor of The Living Wilderness. Zahniser was the primary author of the Wilderness Act passed by Congress in 1964.

Zahniser was born in Franklin, Pennsylvania, to a family that had migrated from Germany in the 1750s. His father was a Free Methodist minister. He grew up in nearby Tionesta along the banks of the Allegheny River close to the Allegheny National Forest. He attended college at Greenville College in Greenville, Illinois, where he graduated with a B.A. degree in English in 1928.

Zahniser began his career on the staff of the United States Bureau of Biological Survey (1930) (now part of the United States Fish and Wildlife Service of the Department of the Interior).

He also became active in private efforts to conserve undeveloped areas. Ten years after The Wilderness Society was founded, Zahniser was hired as their executive secretary, and later worked as executive director. He served as editor of their journal, The Living Wilderness, from 1945 through 1964.

The United States Bureau of Reclamation plans for a ten-dam, billion dollar Colorado River Storage Project began to arouse opposition in the early 1950s when it announced that one of the proposed dams would be at Echo Park, in the middle of Dinosaur National Monument. The controversy assumed major proportions, dominating conservation politics for years. David Brower, executive director of the Sierra Club, and Zahniser representing The Wilderness Society led an unprecedented nationwide campaign to preserve the free-flowing rivers and scenic canyons of the Green and Yampa rivers. They worried that damaging a national monument would be a bad precedent for attempts to preserve other wilderness areas.

Powerful members of Congress and their constituents in western states were committed to the Colorado River Storage Project in order to secure water rights, obtain cheap hydroelectric power, and develop reservoirs as tourist destinations for recreation. After much debate, Congress settled on a compromise that eliminated Echo Park Dam and authorized the rest of the project. The Colorado River Storage Project Act became law on April 11, 1956. It stated, "that no dam or reservoir constructed under the authorization of the Act shall be within any National Park or Monument."

Historians view the Echo Park Dam controversy as marking the start of an era that resulted in increased efforts to conserve wilderness areas. National campaigns resulted in such major conservationist political successes as the Wilderness Act of 1964 and the Wild and Scenic Rivers Act.

In his capacity with The Wilderness Society, Zahniser drafted the Wilderness Act in 1956, which was introduced in the United States Congress that same year — in the House of Representatives by Congressman John P. Saylor of Pennsylvania, and in the Senate by Hubert Humphrey of Minnesota. Zahniser was the main proponent of the Wilderness Act over the subsequent eight years that it took to pass the legislation, including overseeing numerous rewrites, attending all 18 public hearings on the bill, and personally lobbying virtually every member of Congress in support of the legislation.