The Enneagram personality theory was first developed by Oscar Ichazo in 1931, and it was later modernized by psychiatrist Claudio Naranjo and a group of Jesuit priests. With their new findings on the study, psychologist Don Riso and Russ Hudson formed the Enneagram Institute, which has improved apon the theory and now brings it to us in its most modern form.
There are 9 types of personalities, each defined by a certain ego fixation, i.e. psychological need. Although each of the 9 types are active within you, one ego fixation will be so strong or deeply ingrained within you that it will determine your personality.
Ego fixations of the 9 types include:
Type 1: The Reformer - To be good, to have integrity, to be balanced.
Type 2: The Helper - To feel loved.
Type 3: The Achiever - To feel valuable and worthwhile.
Type 4: The Individualist - To find themselves and their significance (to create an identity).
Type 5: The Investigator - To be capable and competent.
Type 6: The Loyalist - To have security and support.
Type 7: The Enthusiast - To be satisfied and content—to have their needs fulfilled.
Type 8: The Challenger - To protect themselves (to be in control of their own life and destiny).
Type 9: The Peacemaker - To have inner stability "peace of mind."
The theory of "wings" states that each type can overlap a bit with the personality type directly adjacent to it, i.e. a type 1 can have a 2 wing or a 9 wing; a type 2 can have a 1 wing or a 3 wing. This is usually shorted to, for instance, 1w2 if you are a 1 with a 2 wing, or 2w1 if you are a 2 with a 1 wing.
The theory of "instincts" states that each person, no matter what type they are, has a mix of the three psychological instincts: Sexual, Social, and Self Preservation. This is one of the reasons why two people can be the same type, but very different. The Sexual Instinct, often referred to as SX, causes you to seek out intense connections in one-on-one relationships. The Social Instinct, often referred to as SO, causes you to seek out warm, open, personal connections with many different people. The Self Preservation Instinct, often referred to as SP, causes you to seek out the safety, comfort, health, energy, and well-being of the physical body. The order in which each instinct is most active in you is referred to as your "stacking," and is often separated by slashes, ie. sx/sp/so or sp/so/sx. To really understand the instincts, you should read the full description here. On a side note, your variant stackings may change when you are in different situations or different levels of health.
One of the wonderful things the Enneagram personality theory does is to analyze nine different levels of healthiness for each personality type. It is amazing how people of the same personality type can be so different when one is functioning on a healthy level and the other is functioning on an unhealthy level. That is why this personality study is just as applicable to, lets say, criminals, as it is to models of society.
The nature of healthiness levels is generally the same over time. A person may fluctuate during the day between healthy, average, and unhealthy levels, but generally they "live" in one state. This state can change only over long periods of time. For instance, a person who is depressed most of the time may have an hour's worth of reborn hope and excitement about the world, only to return after that brief moment to the state in which she normally operates. It is only over long periods of time that she can actually move from functioning at an unhealthy level to functioning at an average level.
|Direction of Integration (Growth)||Direction of Disintegration (Stress)|
An interesting way the Ennegram analyzes stages of health is in the Directions of Integration, when a personality type is experiencing growth to a healthier level, and the Direction of Disintegration, which is the opposite. These directions are the reason for the enneagram shape. A type 4, for instance, behaves like an healthy 1, objective and principled, when she is improving in her level of psychological health. But she becomes like an average 2, over-involved and clinging, when she is under stress, decreasing in her level of psychological health. These directions are indicated by the arrows.
Besides the Direction of Integration and Disintegration, there is an in-between level of movement known as a "Security" point. When a type 4, for instance, feels secure with her situation, but she is not actually undergoing a period of growth in her psychological health, she still becomes more like a type 1, but not on a healthy level; she instead becomes like an average type 1, critical and demanding. The descriptions on Udit Patel's page describe the process for each personality well.
The Enneagram personality study is a deep and complex one. Often you cannot be certain what personality you are by simply reading the token descriptions. Even tests can be faulty. I would recommend first taking the test found here, which is purported to be the most accurate. Then read the information I have gathered for each of the Types from many different sources: 1 2 3 4 5 6 7 8 9. If you still need more information, see my Type Descriptions Resources, which links to each of my sources.
It can be hard to type yourself because the Enneagram Institute constantly talks about the deep, inner motivations of the types, which may be subconscious processes that are unknown to you. A more down-to-earth description can be found on EnneagramSpirituality.com, which features work based on a study by Palmer (whereas the EnneagramInstitute.com is based on studies by Riso and Hudson). Palmer's descriptions (and funny caricatures) may give you more of a "feel" of each type.
The personality types are grouped into "triads." 2, 3, and 4 are in the Heart Triad; 5, 6, and 7 are in the Thinking/Head Triad; and 8, 9, and 1 are in the Instinctive/Gut Triad. The personalities in each of these triads are usually making decisions based either on relationships and emotions (Heart Triad), logic and mental processes (Thinking Triad), or gut and action-oriented processes (Instinctive Triad). Read the full description for a full understanding of the triads.
There is also a more subtle element of the Enneagram personality theory called a "trifix." It basically states that your personality may be subtly influenced not only by your primary personality type, but also by two other personality types in the opposing triads. So if you are a type 4, which is in the Heart Triad, but you also identify strongly with the description of a type 6, which is in the Head Triad, and you notice yourself consistently acting much like a type 1, which is in the Instinctive Triad, then your trifix will be something like 4/6/1. Type 4 personality characteristics are your ego's "primary fixation" and type 6 personality characteristics are you ego's "co-fixation," while type 1 personality characteristics also provide a frame of mind for your ego to become fixated on.
One quote explains the nature of the trifix this way: "The Ego is like a fearful entity living inside the nine-sided house who becomes convinced that the outside is dangerous and that it is most likely to see and be able to respond to this perceived danger by looking through three particular windows. Because the Ego is very fearful, it spends a great deal of time fixated on the view through these three windows. It may set up chairs with binoculars in front of these windows; it will become very familiar with these three particular views. Every time the Ego feels particularly or suddenly threatened, it will immediately go to these windows. The Ego is Fixated in these three Domains. "
Of course, the trifix is a smaller aspect of the Enneagram theory and should not concern you if you are only just starting to determine your type. Only later when you notice some consistent characteristics in yourself which are similar to personalities in other triads should you become interested in finding out your trifix.