The Enneagram is a personality typing system used in psychology. It is a nine-pointed figure, with each point representing one of nine basic personality types. It is usually attributed to Brazilian thinker Oscar Ichazo, who began in the 1950s to develop the theories that would eventually lead to the Enneagram. Ichazo's students, especially Claudio Naranjo, further developed and elaborated on the model beginning in the 1970s.

The Enneagram is intended as a tool of self-discovery, the idea being that one can recognize and avoid the pitfalls of unhealthy behavior patterns by learning about one's type and how it typically responds to stresses. Some psychologists and scientists criticize the Enneagram for its lack of falsifiability, but other more widely accepted personality typologies, such as that developed by Carl Jung, have the same weakness. Recent research in neuroscience suggests biological evidence for the Enneagram, but not all neuroscientists are in agreement on this issue. Critics believe that more research is necessary before the Enneagram can be accepted. A number of companies, including Motorola, Boeing, and the Stanford Master of Business Administration (MBA) program, use the Enneagram to evaluate applicants.

Following is a brief description of the nine personality types. The terminology used to label the triads and types is not standardized, and many different terms may be found in different sources.

Types Two through Four are known as the Feeling triad. Two, The Helper, over-expresses feeling and tends to be compassionate, generous, manipulative, and possessive. Three, The Achiever, is most out of touch with feeling and is characterized by being adaptable, confident, competitive, and critical. Four, The Individualist under-expresses feeling and is typically intuitive, creative, depressive, and introverted.

Types Five through Seven are collectively called the Thinking triad. Five, The Observer, is characterized by over-expressing thought and exhibits analytical, curious, withdrawn, and detached personality traits. Six, The Loyalist, is least in touch with thought and tends to be faithful, responsible, passive-aggressive, and self-doubting. Seven, The Adventurer is prone to under-expressing thought and is enthusiastic, spontaneous, fickle, and narcissistic.

Types Eight, Nine, and One are known as the Instinctive triad. Eight, The Leader, over-expresses instinct and is said to be dominant, decisive, overbearing, and confrontational. Nine, The Peacemaker, is the type most out of touch with instinct, characterized by being perceptive, empathetic, unresponsive and repressed. One, The Perfectionist tends to under-express instinct and is typically idealistic, conscientious, judgemental, and inflexible.

The nine-pointed Enneagram incorporates both a hexagon, connecting types One, Two, Four, Five, Seven, and Eight; and a triangle, connecting types Three, Six, and Nine. The lines that make up these shapes can be used to predict the behavior of each personality type at times of stress or security. These directions are often indicated on the diagram with arrows. The direction of integration, exhibited by personalities at their best, is seen in the sequences 1-4-2-8-5-7-1 and 3-6-9-3. The direction of disintegration is the opposite direction. For example, a Four personality at her best will exhibit traits associated with type Two, while she will exhibit the traits of type One at her most unhealthy.