A Course in Miracles (also referred to as ACIM) is a 1976 book by Helen Schucman. The underlying premise is that the greatest "miracle" is the act of simply gaining a full "awareness of love's presence" in a person's life. Schucman said that the book had been dictated to her, word for word, via a process of "inner dictation" from Jesus Christ. The book is considered to have borrowed from New Age movement writings. The book has been called everything from "New Age psychobabble" to "a Satanic seduction" to "The New Age Bible".

Throughout the 1980s, annual sales of the book steadily increased. According to Olav Hammer, the psychiatrist and author Gerald G. Jampolsky was among the most effective promoters of ACIM. Jampolsky's first book, Love is Letting Go of Fear, based on the principles of ACIM, was published in 1979 and, after being endorsed on Johnny Carson's show, sold over three million copies by 1990. The largest growth in sales occurred in 1992 after Marianne Williamson discussed the book on The Oprah Winfrey Show, with more than two million volumes sold.

A Course in Miracles was written as a collaborative venture between Schucman and psychologist William ("Bill") Thetford. In 1958, Schucman began her professional career at Columbia–Presbyterian Medical Center in New York City as Thetford's research associate. In 1965, at a time when their weekly office meetings had become so contentious that they both dreaded them, Thetford suggested to Schucman that "[t]here must be another way". Schucman believed that this interaction acted as a stimulus, triggering a series of inner experiences that were understood by her as visions, dreams, and heightened imagery, along with an "inner voice" that she identified as Jesus (although the ACIM text itself never explicitly claims that the voice she hears speaking is that of Jesus). She said that on October 21, 1965, an "inner voice" told her: "This is a Course in Miracles, please take notes."

Schucman said the writing made her very uncomfortable, though it never seriously occurred to her to stop. The next day, she explained the events of her "note-taking" to Thetford. To her surprise, Thetford encouraged her to continue the process. He also offered to assist her in typing out her notes as she read them to him. The process continued the next day and repeated regularly for many years. In 1972, the writing of the three main sections of ACIM was completed, with some additional minor writing coming after that point.

For copyright purposes, US courts determined that the author of the text was Schucman, not Jesus. Kenneth Wapnick, psychologist, devotee and teacher of the ACIM, believed that Schucman did not channel Jesus, but was describing her "own mental experience of divine 'love'".

ACIM has three sections: "Text", "Workbook for Students", and "Manual for Teachers". Written from 1965 to 1972, some distribution occurred via photocopies before the Foundation for Inner Peace published a hardcover edition in 1976. The copyright and trademarks, which had been held by two foundations, were revoked in 2004 after lengthy litigation because the earliest versions had been circulated without a copyright notice.

In ACIM, it is written that "the ego's death is your life." The ego is presented as a non-entity, an illusion that ceases to exist once one lays it down: "When you have given up the illusion of the ego, you will realize that the ego never existed, and that the only thing that ever existed, and still exists, is God and His creations." Therefore, in ACIM, the ego is simply an illusion that appears to obscure one's oneness with God and his creations, not an essential part of oneself. To summarize the effects of letting go of the ego, it is written, "When the ego has been dispelled, there will be no separation, and you will be wholly real," "real" referring to being in alignment with God and how he created the reader.

Since it went on sale in 1976, the book has been translated into 27 languages. It is distributed globally, spawning a range of organized groups.