The Wilderness Act of 1964 (Pub.L. 88–577) was written by Howard Zahniser of The Wilderness Society. It created the legal definition of wilderness in the United States, and protected 9.1 million acres (37,000 km²) of federal land. The result of a long effort to protect federal wilderness and to create a formal mechanism for designating wilderness, the Wilderness Act was signed into law by President Lyndon B. Johnson on September 3, 1964 after over sixty drafts and eight years of work.
The Wilderness Act is well known for its succinct and poetic definition of wilderness:
A wilderness, in contrast with those areas where man and his own works dominate the landscape, is hereby recognized as an area where the earth and its community of life are untrammeled by man, where man himself is a visitor who does not remain.
When Congress passed and President Lyndon Johnson signed the Wilderness Act on September 3, 1964, it created the National Wilderness Preservation System. The initial statutory wilderness areas, designated in the Act, comprised 9.1 million acres (37,000 km²) of national forest wilderness areas in the United States of America previously protected by administrative orders. The current amount of areas designated by the NWPS as wilderness totals 757 areas encompassing 109.5 million acres of federally owned land in 44 states and Puerto Rico (5% of the land in the United States).
This summary is from Wikipedia.