Midi-chlorians were microscopic, intelligent life forms that originated from the foundation of life in the center of the galaxy, and ultimately resided within the cells of all living organisms, thereby forming a symbiotic relationship with their hosts. The Force spoke through the midi-chlorians, allowing certain beings to use the Force if they were sensitive enough to its powers. In order to gauge an individual’s potential in the Force, blood tests were used to estimate the number of midi-chlorians within the subject’s cells. Anakin Skywalker, the Chosen One, possessed the highest known count in galactic history—over twenty-thousand midi-chlorians—surpassing the potential of Grand Master Yoda and all Jedi.

According to the Sith Lord Darth Sidious, his Sith Master Darth Plagueis could influence the midi-chlorians to create life. In the New Republic Era, Imperial scientist Doctor Pershing experimented with blood samples that he harvested from Grogu, a Force-sensitive youngling with a high midi-chlorian count.

Midi-chlorian was the scientific name for a species of sentient and microscopic organisms that inhabited the cells of every life form. Their existence was integral to the all-encompassing energy field known as the Force, connecting the Living Force to the Cosmic Force. By serving as the link between the two aspects of the Force, the midi-chlorians made it possible to achieve immortality after death. With sufficient training and total immersion in the light side of the Force, the deceased could preserve their identity in the form of a Force spirit after becoming one with the Force.

In addition to their connection with the Force, midi-chlorians lived in a symbiotic relationship with their organic hosts—a bond that was especially strong with Force-sensitive beings, who possessed a high quantity of midi-chlorians in their cells. This mutually advantageous relationship allowed the midi-chlorians to communicate the will of the Force to their Force-sensitive symbionts, who were capable of utilizing the powers of the Force through the midi-chlorians.The more of these tiny organisms a being possessed, the greater potential for power in the force a being had.