Public auditions by aspiring pop singers began in June 2009 and were held in five cities across the United Kingdom. All four series-five judges – Simon Cowell, Dannii Minogue, Louis Walsh, and Cheryl Cole – returned to judge the contestants, with auditions being held in front of a live audience for the first time. Following initial auditions, the "Boot camp" stage took place in August 2009, where the number of contestants was narrowed down to 24. The 24 contestants were split into their categories, Boys, Girls, Over 25s and Groups, and given a judge to mentor them at the "Judges' Houses" stage and throughout the finals.
During "Judges' Houses", the 24 acts were reduced to 12, who went on to the live finals, with one act being eliminated each week by a combination of public vote and judges' decision until a winner was found. The live shows started on 10 October 2009. The acts performed every Saturday night with the results announced on Sundays. This was change of format from previous series in which the results were announced later on the Saturday evening.
The winner's single for this series is a cover version of "The Climb" orginally sung by Miley Cyrus.
As with the auditions, the "Boot camp" selection stage was filmed in front of a live audience. Filming took place on 1 August at the HMV Hammersmith Apollo. Approximately 200 acts attended Boot Camp. They were initially split into groups of three, and judges gave instant decisions on who would leave based on the group performances, bringing the number of acts down to 100. The judges then cut the number of acts down to 50. Following a further set of auditions, the number of contestants was narrowed to 24. Originally, the group Trucolorz were chosen by the judges for the final 24 but were disqualified due to one of the group's members being too young for the show, and they were replaced by Harmony Hood.
The contestants were then split into the usual four categories before the judges discovered which category they would mentor for the rest of the competition. The Boys (16–24) were mentored by Cole, Minogue had the Girls (16–24), Cowell mentored the Over 25s, and Walsh took charge of the Groups.
Each judge had help from a guest judge during the "Judges' Houses" stage. Will Young assisted Cole in Marrakech, Morocco, Minogue had help from her sister Kylie Minogue in Atlantis, The Palm, Dubai, Boyzone singer Ronan Keating helped Walsh near Lake Como in Italy, and Cowell had help from Sinitta in Los Angeles. At Judges' Houses, each act sang for their respective judge, and each judge and their guest eliminated three acts, leaving 12 acts to perform in the live shows.
Girls: Nicole Jackson, Stacey McClean, Despina Pilavakis
Over 25s: Treyc Cohen, Nicole Lawrence, Daniel Pearce
Groups: De-Tour, Harmony Hood, Project A