In theistic traditions, mysticism is often described as a “unitive” experience of love and communion with God. In non-theistic traditions, such as Buddhism, it is an intuitive or contemplative approach to understanding some ultimate reality and thereby having a renewed understanding of what is really real. In either case, it is understood as an experience beyond ordinary experience and reason. This does not necessarily mean, however, that the experience is antagonistic to logic or reason.

Mystics in the Roman Catholic tradition claim that the soul undergoes a purification (often called the purgative way), which leads to a feeling of illumination and greater love of God (the illuminative way). After a time, the soul may be said to enter into mystical union with God (the unitive way), which begins with consciousness that God is present to the soul. The soul progresses through a time of quiet and an ecstatic state to a final state of perfect union with God, which is sometimes referred to as a spiritual marriage.

Examples of such mystical experiences are plentiful throughout the world's religions. People who have had the experiences insist that they are not fully accessible by just reading about them. One can't intellectualize the experience, for the mystical experience is not just a state of knowing. Reading mystical literature — whether those detailing the vivid descriptions of Teresa of Avila or those of the Muslim Al-Ghazzali — is only an indirect approach to the experience. The direct approach must be one where the subject is unified with the object and transcends the subject-object divisions of everyday life.

Some maintain that mysticism is the heart of all religion and even a key to the unity of all religions. As such, religions prescribe techniques of contemplation and meditation.