Marilyn Ferguson (April 5, 1938 – October 19, 2008) was an American author, editor and public speaker known for her 1980 book The Aquarian Conspiracy, which is connected with the New Age Movement.

Ferguson published and edited the well-regarded science newsletter Brain/Mind Bulletin from 1975 to 1996. She eventually earned several honorary degrees, served on the board of directors of the Institute of Noetic Sciences, and befriended such diverse figures of influence as inventor and theorist Buckminster Fuller, spiritual author Ram Dass, Nobel Prize-winning chemist Ilya Prigogine and billionaire Ted Turner. Ferguson's work also influenced Vice President Al Gore, who participated in her informal network while a senator, and later met with her in the White House.

Ferguson was born Marilyn Louise Grasso in Grand Junction, Colorado. After graduation from high school she earned an associate of arts degree at Mesa College (now Colorado Mesa University) and later attended the University of Colorado. During her first marriage, to Don Renzelman, she worked as a legal secretary and became a published author of short stories and poetry in such national magazines as Cosmopolitan. Later she wrote freelance articles for Time and other publications. After living briefly in Houston, Texas, she moved to California with her second husband, Mike Ferguson, in 1968. That year, she published her first book, on home economics, with her husband as co-author.

Ferguson soon developed an enduring interest in what came to be known as the "human potential" movement, and particularly the latest research on the potential of the human brain, with its implications for learning, creativity and wellness.

This inspired her to write The Brain Revolution: The Frontiers of Mind Research (Taplinger, 1973), a successful and broadly hailed popular summary of these discoveries. Two years later Ferguson launched Brain/Mind Bulletin, a newsletter that served as an ongoing forum for her interest in cutting-edge scientific ideas. At its peak in the 1980s the publication had a worldwide base of some 10,000 subscribers, ranging from academics and intellectuals to schoolteachers and storekeepers, and helped to popularize the ideas of such notables as Prigogine, neuroscientists Karl Pribram and Candace Pert, physicists Fritjof Capra and David Bohm, psychologist Jean Houston and many others.

The magazine sold ad space to New Age advertisers.

In an early commentary in the newsletter Ferguson described her first glimmers of what she called "the movement that has no name" - a loose, enthusiastic network of innovators from almost every discipline, united by their apparent desire to create real and lasting change in society and its institutions. Her attempt to compile and synthesize the patterns she was seeing eventually led her to develop a second newsletter, Leading Edge Bulletin, and found its culmination in The Aquarian Conspiracy (J.P. Tarcher, 1980), the seminal work that earned her a lasting global reputation.

The book's title led to some confusion, having to do with astrology only to the extent of drawing from the popular conception of the "Age of Aquarius" succeeding a dark "Piscean" age. The word conspiracy she used in its literal sense of "breathing together," as one of her great influences, the philosopher Pierre Teilhard de Chardin, had done before her.