A species of microscopic organism. It is a symbiotic creature that exists within the cells of every living creature. Life in the galaxy is dependent upon the Midi-Chlorians. There is no pattern which dictates the concentration of midi-chlorians in a being’s make-up, but a higher count of midi-chlorians in a being’s cells allows them to touch the Force. As the count increases, so does the being’s ability to connect with the Force.

Midi-Chlorians are intelligent; they have wills. Midi-Chlorians need organic life to exist and visa versa. This relationship creates a Universal Energy Field. Therefore every living thing is connected with every other living thing through this Field. The Force is a "Oneness", a kind of communal awareness that beings can tap into. This Oneness contains all of the knowledge of the galaxy and transcends the concept of space. This allows those who access the Oneness to gain knowledge of the past, the present and possible futures.

Part of the brain of every sentient being is "locked" or inaccessible for most beings and is thus unable to be utilized. It is this part of the brain that is responsible for allowing a person to have extrasensory skills such as TK, ESP, levitation, and empathy.

In the course of the relationship between Midi-Chlorians and the living beings they inhabit the Midi-Chlorians access the part of the brain that is normally inaccessible and "unlock" it. This allows the person to use those "personal" Force skills - ESP, TK, empathy, levitation, and so on. This also explains how people get certain impulses like Deja Vue's.