The term "enneagram" derives from two Greek words, ennea (nine) and grammi (line). The Enneagram is a nine-pointed figure inscribed in a circle. The meaning of the symbol itself, together with the personality types organized around the nine points, convey a system of "knowledge" about nine distinct but interrelated personality types, or nine ways of seeing and experiencing the world. The Enneagram of Personality is generally presented as a psychospiritual system for mapping and understanding nine possible personality types. Each personality type associated with the Enneagram represents a map of traits that highlights patterns of thinking, feeling, and behaving. By learning one's type and the patterns and habits associated with that type, one can use the Enneagram system as an effective tool for self-understanding and self-development.

Adherents of the theory believe that each Enneagram personality type, or style, is based on a pattern of where attention goes. They believe that by learning about what kinds of things one habitually attends to and puts energy into, one can observe oneself more accurately and develop more self-awareness, and that by enhancing one's self awareness with the help of the Enneagram, one can exercise more choice about one's functioning rather than engaging in patterns of thought, emotion, and behavior in an automatic, habitual, unconscious way.

The enneagram figure possibly originated around 2500 BC. It was first brought to the attention of the modern world by G. I. Gurdjieff, the originator of a school of spiritual work near Paris in the 1930s. Although Gurdjieff used the Enneagram diagram to describe possibilities of human development, his concept of the diagram was related to the symbolic communication of ancient knowledge and the "self-work" process through which individuals can acquire insight rather than to the categorizing of personality styles. Oscar Ichazo assigned descriptions to each of the nine positions on the Enneagram diagram he called the Enneagram of Ego Fixations, which was the origination of the Enneagram of Personality as we know it today. The popular use of the Enneagram of personality began principally with Claudio Naranjo who had studied with Ichazo in Chile but was asked to leave before the intensive 1971 training had finished. He took Ichazo's teaching and further developed it, articulating the nine types in Western psychological terms. Naranjo then brought his understanding of the Enneagram system to Berkeley (the city, not the university) in the early 1970s, where he taught it to students in the context of his own program of self-development work.

According to Enneagram of Personality theory, the points of the enneagram figure indicate a number of ways in which nine principal ego-archetypal forms or types of human personality ("Enneatypes") are psychologically connected. People of each Enneatype are usually referred to after the number of the point on the enneagram figure (Eights, Fours, Sixes etc.) that indicates their particular psychological space and 'place' of connection to the other types. They are also often given names that suggest some of their more distinctive archetypal characteristics.

The nine Enneagram types are grouped into three groups of three, corresponding to the three Centers of Intelligence, through which information is processed (head, heart, and body) and the three core emotions (fear, grief, and anger). In the West, the head is commonly considered the only Center of Intelligence, but the Enneagram highlights the importance of the emotions and the body as equally important centers of functioning and interacting with the outside world.

According to the Enneagram system, each of the nine types is limited by an imbalance involving one of the three Centers of Intelligence. The human faculty primarily involved with the Head Center is thinking, the faculty primarily involved with the Emotional Center is feeling, and the faculty primarily involved with the Body Center is will. Each of the head types has a different kind of imbalance involving thinking, each of the heart types a different kind of imbalance involving feeling, and each of the body types a different kind of imbalance involving will.

The three Centers of Intelligence also correspond to three core emotions that influence the character of the types. The head types (5, 6, and 7) are also the fear types, and their personality style is shaped by their relationship to fear. The heart types (2, 3, and 4) are also the grief or sadness types, and their personality style is fundamentally shaped by their relationship to grief. The body types (8, 9, and 1) are the anger types, and their personality is fundamentally shaped by their relationship to anger. The types on the inner triangle (3, 6, 9) are also called the core points of each center's triad of types. Thus, type 3 is the core of the Heart Center types; type 6 is the core of the Head Center types; and type 9 is the core of the Body Center types.

Each Enneagram type may be influenced by the types on either side of it (adjacent to it). These two types are known as wings of the type, and may or may not color the expression of a given individual's personality type or core point. The circle of the Enneagram symbol suggests that the types or points exist on a spectrum, rather than as distinct types or points unrelated to those adjacent to them. Thus, an individual may be said to have a core point and one wing, two wings, or both wings that influence but do not change that person's core type.