On American Idol, each season premieres with the audition round, which take place in different cities across the United States. The audition episodes typically feature a mix of potential finalists, interesting characters and woefully inadequate contestants. Each successful contestant receives a golden or platinum ticket to proceed on to the next round in Hollywood. Based on their performances during the Hollywood round (Las Vegas round from 2011 to 2013), 24 to 36 contestants are selected by the judges to participate in the semifinals. From the semifinals onward, the contestants perform their songs live, with the judges making their critiques after each performance. The contestants are voted for by the viewing public, and the outcome of the public votes is then revealed during a results segment. The results segment feature group performances by the contestants as well as guest performers. The Top 3 results also features homecoming events for the Top 3 finalists. The season reaches its climax in a two-hour results finale show, where the winner of the season is revealed.

With the exception of the first two seasons, the contestants in the semifinals onward perform in front of a studio audience. They perform with a full band in the finals. The current musical director is Kris Pooley, who has been with the show since the ABC revival began in 2018. In previous seasons, the Idol band was led by Rickey Minor, who initially served from 2005 to 2010; Minor left the show in 2010 to become musical director for The Tonight Show with Jay Leno. Minor was replaced by Ray Chew, who served from 2011 to 2013. Chew left the show in late 2013 to become musical director for Dancing with the Stars, where he has remained ever since. In February 2014, The Tonight Show with Jay Leno ended, and Minor returned to American Idol where he again served as musical director. Minor remained on the show until the original version ended in April 2016. Assistance has also been given by vocal coaches and song arrangers, such as Michael Orland and Debra Byrd to contestants behind the scene.

Starting with the seventh season in 2008, contestants may perform with a musical instrument from the Hollywood rounds onward. In later seasons, the contestants were allowed to perform with a musical instrument in the auditions. From the shows' inception in 2002 until 2010, performance shows were usually aired live on Tuesday nights, followed by the results shows on Wednesday night. In 2011, however, the performance shows were moved to Wednesday nights and the results shows on Thursday nights, which remained until the fourteenth season began in 2015 (with the exception of the finales of season ten, eleven and thirteen, where the performance shows and results shows reverted to Tuesday nights and Wednesday nights, respectively).

In 2015, starting with the fourteenth season, the show discontinued separate results shows, with both performance and result shows airing on the same night. This rule has been in place ever since. On the fourteenth season, the show aired on Wednesday nights, and on the fifteenth season, the show aired on Thursday nights. Since the ABC revival began in 2018, the show has been airing on Sunday nights and Monday nights, though both nights contain performances and do not feature separate results shows.[citation needed]

2002–2016: Fox

Season 1 (2002)

The first season of American Idol debuted as a summer replacement show in June 2002 on the Fox network. It was co-hosted by Ryan Seacrest and Brian Dunkleman. Randy Jackson, Paula Abdul, and Simon Cowell served as judges.

In the audition rounds, 121 contestants were selected from around 10,000 who attended the auditions. These were cut to 30 for the semifinal, with ten going on to the finals. One semifinalist, Delano Cagnolatti, was disqualified for lying to evade the show's age limit. One of the early favorites, Tamyra Gray, was eliminated at the top four, the first of several such shock eliminations that were to be repeated in later seasons. Christina Christian was hospitalized before the top six result show due to chest pains and palpitations, and she was eliminated while she was in the hospital. Jim Verraros was the first openly gay contestant on the show; his sexual orientation was revealed on his blog, but it was removed during the competition after a request from the show producers over concerns that it might be unfairly influencing votes.

The final showdown was between Justin Guarini, one of the early favorites, and Kelly Clarkson. Clarkson was not initially thought of as a contender, but impressed the judges with some good performances in the final rounds, such as her performance of Aretha Franklin's "Natural Woman", and Betty Hutton's "Stuff Like That There", and eventually won the crown on September 4, 2002.

In what was to become a tradition, Clarkson performed the coronation song during the finale, and released the song immediately after the season ended. The single, "A Moment Like This", went on to break a 38-year-old record held by The Beatles for the biggest leap to number one on the Billboard Hot 100. Guarini did not release any song immediately after the show and remains the only runner-up not to do so. Both Clarkson and Guarini made a musical film, From Justin to Kelly, which was released in 2003 but was widely panned. Clarkson has since become one of the most successful Idol contestants internationally, with worldwide album sales of more than 25 million.

Starting September 30, 2006, this season was repackaged as "American Idol Rewind" and syndicated directly to stations in the U.S.

Season 2 (2003)

Following the success of the first season, the second season was moved up to air in January 2003. The number of episodes increased, as did the show's budget and the charge for commercial spots. Dunkleman left the show, leaving Ryan Seacrest as the lone host. Randy Jackson, Paula Abdul, and Simon Cowell returned as judges. Kristin Adams was a correspondent for this season.

Corey Clark was disqualified during the finals for having an undisclosed police record; however, he later alleged that he and Paula Abdul had an affair while on the show and that this contributed to his expulsion. Clark also claimed that Abdul gave him preferential treatment on the show due to their affair. The allegations were dismissed by Fox after an independent investigation. Two semi-finalists were also disqualified that year – Jaered Andrews for an arrest on an assault charge, and Frenchie Davis for having previously modeled for an adult website.

The season finale drew more than 38 million viewers, marking Idol'''s biggest audience ever for a single episode. Ruben Studdard emerged as the winner, beating Clay Aiken by a small margin. Out of a total of 24 million votes, Studdard finished just 134,000 votes ahead of Aiken. This slim margin of victory was controversial due to the large number of calls that failed to get through. In an interview prior to the fifth season, executive producer Nigel Lythgoe indicated that Aiken had led the fan voting from the wildcard week onward until the finale.

Both finalists found success after the show, but Aiken out-performed Studdard's coronation song "Flying Without Wings" with his single release from the show "This Is the Night", as well as in their subsequent album releases. The fourth-place finisher Josh Gracin also enjoyed some success as a country singer.

Season 3 (2004)

The third season premiered on January 19, 2004. Ryan Seacrest returned as host, and Randy Jackson, Paula Abdul, and Simon Cowell returned as judges. One of the most talked-about contestants during the audition process was William Hung whose off-key rendition of Ricky Martin's "She Bangs" received widespread attention. His exposure on Idol landed him a record deal and surprisingly he became the third bestselling singer from that season.

Much media attention on the season had been focused on the three black singers, Fantasia Barrino, LaToya London, and Jennifer Hudson, dubbed the Three Divas. All three unexpectedly landed on the bottom three on the top seven result show, with Hudson controversially eliminated. Elton John, who was one of the mentors that season, called the results of the votes "incredibly racist"., Reuters via Yahoo.com, 2004-04-28, Retrieved on March 2, 2007. The prolonged stays of John Stevens and Jasmine Trias in the finals, despite negative comments from the judges, had aroused resentment, so much so that John Stevens reportedly received a death threat, which he dismissed as a joke 'blown out of proportion'.

The performance of "Summertime" by Barrino, later known simply as "Fantasia", at Top 8 was widely praised, and Simon Cowell considered it as his favorite Idol moment in the nine seasons he was on the show. Fantasia and Diana DeGarmo were the last two finalists, and Fantasia was crowned as the winner. Fantasia released as her coronation single "I Believe", a song co-written by the first season finalist Tamyra Gray, and DeGarmo released "Dreams".

Season 4 (2005)

The fourth season premiered on January 18, 2005. Ryan Seacrest returned as host, and Randy Jackson, Paula Abdul, and Simon Cowell returned as judges. This was the first full season of the series to be aired in high definition; the finale of the third season was also aired in high definition. The number of those attending the auditions by now had increased to over 100,000 from the 10,000 of the first season. The age limit was raised to 28 in this season, and among those who benefited from this new rule were Constantine Maroulis and Bo Bice, the two rockers of the show.

The top 12 finalists originally included Mario Vazquez, but he dropped out citing 'personal reasons' and was replaced by Nikko Smith. Later, an employee of Fremantle Media, which produces the show, sued the company for wrongful termination, claiming that he was dismissed after complaining about lewd behavior by Vazquez toward him during the show.

During the top 11 week, due to a mix-up with the contestants' telephone number, voting was repeated on what was normally the result night, with the result reveal postponed until the following night.

In May 2005, Underwood was announced the winner, with Bice the runner-up. Both Underwood and Bice released the coronation song "Inside Your Heaven", with Underwood's version of the song making her the first country artist ever to debut at number-one on the Billboard Hot 100 chart. As of 2015, Underwood has become the most successful Idol contestant in the U.S., selling 16 million albums in the country, while selling a total of 65 million records worldwide.

Season 5 (2006)

The fifth season began on January 17, 2006. Ryan Seacrest returned as host, and Randy Jackson, Paula Abdul, and Simon Cowell returned as judges. It remains the highest-rated season in the show's run so far. Two of the more prominent contestants during the Hollywood round were the Brittenum twins who were later disqualified for identity theft.

Chris Daughtry's performance of Fuel's "Hemorrhage (In My Hands)" on the show was widely praised and led to an invitation to join the band as Fuel's new lead singer, an invitation he declined. His performance of Live's version of "I Walk the Line" was well received by the judges but later criticized in some quarters for not crediting the arrangement to Live. He was eliminated at the top four in a shocking result.

On May 30, 2006, Taylor Hicks was named American Idol, with Katharine McPhee the runner-up. "Do I Make You Proud" was released as Hicks' first single and McPhee's was "My Destiny".

Despite being eliminated earlier in the season, Chris Daughtry (as lead of the band Daughtry) became the most successful recording artist from this season. Other contestants, such as Hicks, McPhee, Bucky Covington, Mandisa, Kellie Pickler, and Elliott Yamin have had varying levels of success.

Season 6 (2007)