UFC 47: It's On! was a mixed martial arts event held by the Ultimate Fighting Championship on April 2, 2004 at the Mandalay Bay Events Center in Las Vegas, Nevada. The event was broadcast live on pay-per-view, and later released on DVD.

Headlining the card was the long awaited match between Chuck Liddell and Tito Ortiz.

The title "It's On!" refers to Chuck Liddell and Tito Ortiz' long running negotiations leading up to the fight. Fans had been awaiting the fight for more than a year, and while both fighters had their own story as to why it took so long, the fight finally took place in 2004. Ortiz claims that as friends and former training partners, he and Liddell had made a pact never to fight. Liddell claims there was no such pact, that he would fight anyone anytime, and accused Ortiz of ducking the fight.

A matchup between Tim Sylvia and Andrei Arlovski for the then-vacant UFC Heavyweight Championship was scheduled for this event, but Sylvia was pulled due to a reoccurence of positive drug samples just a day before the event. Arlovski was re-booked on short notice in a non-title fight against Wesley Correira, who was pulled from a scheduled main card fight with Mike Kyle to replace Sylvia. Wes Sims would step in on a day's notice to face Mike Kyle at this event as well. The Sylvia/Arlovski matchup would finally be re-booked for the Interim Heavyweight Championship at UFC 51 in February 2005, with Arlovski winning via submission.

Nicholas Robert Diaz (born August 2, 1983) is a American mixed martial artist of Mexican descent. He is the former Strikeforce Welterweight Champion, WEC and IFC Welterweight Champion. He has competed in the Ultimate Fighting Championship, Pride Fighting Championships and Elite Xtreme Combat. Diaz was promoted to black belt in Brazilian Jiu-Jitsu by Cesar Gracie on May 8, 2007. Diaz trains at the Diaz brother's Cesar Gracie Jiu-Jitsu Academy in Lodi, California. Diaz holds the distinction of having never been submitted, and has been finished by strikes only once in 35 fights. He is currently ranked the #4 welterweight in the world by Sherdog, ESPN, MMAWeekly, and USA Today.

Diaz was born in Stockton , California. He is the older brother of UFC fighter Nate Diaz. He went to Tokay High School in Lodi for one year before dropping out. While a freshman, he was a member of the swimming team. Diaz has stated in the past that he is thankful his mother got him into swimming classes because swimming is one of the main reasons why his cardio is so impressive during his fights. Diaz has also said on multiple occasions that he had a hard childhood and grew up without his biological father.

Charles David "Chuck" Liddell (born December 17, 1969) is a retired American mixed martial artist and former Ultimate Fighting Championship light heavyweight champion. Liddell has an extensive striking background in Kempo, Koei-Kan karate and kickboxing, as well as a grappling background in collegiate wrestling. Liddell is known for his Knockout power, Iron chin, Excellent counter striking and for his sprawl-and-brawl technique, which made him one of the most difficult fighters to takedown. He is one of the most dominant champions that ever competed in the UFC. He still holds the record for the most knockouts in UFC history. As of his retirement, Liddell has had 23 fights in the UFC. Along with fellow UFC Hall of Fame fighter Randy Couture, Liddell is widely credited for bringing mixed martial arts into the mainstream of American sports and entertainment. On July 10, 2009, he was inducted into the UFC Hall of Fame.

Liddell began studying Koei-Kan karate at the age of 12; the tattoo seen on his scalp reads "Koei-Kan". Liddell was a four-year starter on the football team at San Marcos High School. While growing up in Santa Barbara, he often frequented the infamous Del Playa Drive, the middle of the party scene of the college town of Isla Vista, where he often found himself in fights with drunk college students. He became a Division I wrestler at California Polytechnic State University, San Luis Obispo and graduated with a Bachelor of Arts Degree in Business/Accounting in 1995. He holds an amateur kickboxing record of 20 wins and 2 losses, with 16 of his wins coming by way of knockout.

Jacob Christopher "Tito" Ortiz (English: /tɪtɵ ɔərtɪs/) (born January 23, 1975) is an American mixed martial artist and former UFC Light Heavyweight Champion, having held the title from April 14, 2000 to September 26, 2003. Along with fighters like Randy Couture and Chuck Liddell, he was one of the sport's early stars. Ortiz ultimately became the biggest pay-per-view draw of 2006 for his fights with Liddell, Forrest Griffin, and Ken Shamrock.

Outside of his fighting career, Ortiz is the CEO of the Punishment Athletics MMA equipment and clothing line. He also owns an MMA training gym called Punishment Training Center, which is located in Huntington Beach, CA.

Jacob Christopher Ortiz was born to Samuel and Joyce Ortiz. He received his nickname "Tito," which means tyrant, from his father when he was a year old. He is the fourth child of his mother, Joyce, who had three sons from a previous marriage. His mixed heritage (Mexican father, American mother) has been reflected in his ring entrances as he has borne both Mexican and American flags.

Clayton Charles Guida (pronounced /ˈɡwiːdə/; born December 8, 1981) is an American mixed martial artist and currently fighting in the UFC as a lightweight. Guida was the first Strikeforce Lightweight Champion and held the title until being defeated by Gilbert Melendez at Strikeforce: Revenge. As of October 2011, Guida is ranked as the #8 lightweight fighter in the world by Sherdog and #6 lightweight by MMAWeekly.com.

Guida is renowned for his relentless pressure and unending stamina.

During the early stages of his MMA career, Guida worked as a carpenter (leading to his nickname, "The Carpenter") while training and fighting in his spare time, compiling a professional record of 20-6.

Clay was generous enough to finance the inspirational video played before the state championship matches. He stepped in with the money after the Illinois High School Association was not able to pay for it.^{[unreliable source?]} Clay is a former Illinois wrestler for Johnsburg High School.

Guida was successful in his UFC debut, submitting Justin James in the second round at UFC 64.