James Andrew Miller (born August 30, 1983) is an American professional mixed martial artist. He currently competes in the Lightweight division of the Ultimate Fighting Championship (UFC), where he currently holds the UFC records for most bouts, most total wins, and most wins in the Lightweight division. He is the younger brother of former UFC fighter Dan Miller.

Born and raised in Sparta Township, New Jersey and the youngest of three brothers, Miller started wrestling at the age of four. He competed in wrestling in high school at Sparta High School, as well as one year of collegiate wrestling at Virginia Tech. Miller had not originally planned on wrestling at Virginia Tech, but his desire to compete again grew and he made the team as a walk-on later into the season. However, Miller did not continue competing for the school because of "disagreements" with the coaching staff and the program. He currently holds a black belt in Brazilian jiu-jitsu under Jamie Cruz. Miller began training in mixed martial arts in 2005 at Planet Jiu-Jitsu in Sparta, New Jersey with his brother Dan Miller.

Miller had his first professional fight on November 19, 2005, against Eddie Fyvie at Reality Fighting 10. Miller controlled the fight and earned a unanimous decision. Miller earned two more victories in the promotion over Kevin Roddy and Joe Andujar, both via the first-round submission. The quick victories earned Miller a title shot and he fought Muhsin Corbbrey for the Reality Fighting Lightweight Championship. Miller mounted Corrbrey in the second round and battered his opponent before securing an armbar for the victory. In his first title defense, Miller took on future UFC Lightweight Champion Frankie Edgar at Reality Fighting 14. Edgar controlled the fight, but Miller secured a tight guillotine late in the final round. Edgar fought through the choke to earn the unanimous decision.

In the weeks prior to Reality Fighting 14, Planet Jiu-Jitsu closed down. Miller began training at AMA Fight Club in Whippany, New Jersey with his brother Dan in January 2007.

Miller debuted with the Cage Fury Fighting Championships in a Lightweight Championship bout on April 13, 2007, against Evo Fight Club's Al Buck. Jim fought on the same card as his brother for the first time since Reality Fighting XII and both were victorious. Miller and Buck squared off but were forced to separate early after an accidental knee to Buck's groin. When the fight resumed, Miller began working for a takedown and after escaping an attempted guillotine, secured a slam, from which he quickly attained the mount and then the back, sinking in a rear-naked choke for the win.

Miller defended his title for the first time at Cage Fury Fighting Championships 5 against Atlantic City MMA's Anthony Morrison. Morrison delivered some big slams early, but Miller worked through a chain of submissions before securing the victory by triangle choke at 4:56 of the first round to retain his title.

Miller's second defense was scheduled for the Cage Fury Fighting Championships 6 card, where he was to face King of the Cage Champion Clay French, but the event was canceled a week prior to the event when a primary investor dropped out.

Jim and his brother Dan signed with the UFC in July 2008. Miller made his debut at UFC 89 where he defeated David Baron in the third round. This win earned Miller his first Submission of the Night bonus award.