In the Star Wars universe, Midi-chlorians are a microscopic lifeform that reside in all living cells. Living beings supposedly live in symbiotic existence with them. They are believed to be essential for the existence of all life and responsible in particular for the Jedi knowledge of the force.

As is mentioned by Qui-Gon Jinn in the Phantom Menace, they continuously talk to and guide the life forms they reside in. A Jedi knight learns to listen to them by quietening his mind, resulting in what is percieved as the Force.

Anakin Skywalker who later becomes Darth Vader is supposed to have had the largest ever midi-chlorian count in a living being, reaffirming Qui-Gon Jinn's belief that Anakin is indeed 'the chosen one', who would bring back balance to the force. He is believed to have no father and to have been directly concieved by the midi-chlorians through Shmi Skywalker, Anakin's mother.