Cole started his career at his hometown club Arsenal as a teenager, and signed as a professional on 25 February 2000. He had made his debut for the first team as a striker on 30 November 1999 against Middlesbrough at the age of 18, although this was his only appearance of that season. Before he fully broke into the Arsenal side, he spent part of the 1999–2000 season on loan at Crystal Palace, where he played 14 league matches and scored one goal, a long-range half-volley against Blackburn Rovers. After an injury to Sylvinho, Arsenal's established Brazilian left-back, in autumn 2000, Cole came on as his replacement, and remained first-choice even after Sylvinho's recovery.

With Arsenal, he won the Premier League twice (in 2002 and 2004), and the FA Cup three times (in 2002, 2003 and 2005). Although injured for much of the 2005-06 season, he recovered in time to play in Arsenal's UEFA Champions League Final defeat to Barcelona at the end of the season. In total he made 228 first-team appearances for Arsenal, scoring 8 goals.

In 2005, Cole made inappropriate contact with league rivals Chelsea over a possible move, without alerting Arsenal to the fact, in a case of "tapping-up". Found guilty, he was fined £100,000 by the Premier League on 2 June 2005 for a meeting in a hotel in January 2005 between himself, the Chelsea manager José Mourinho, Chelsea chief executive, Peter Kenyon, and his agent Jonathan Barnett. An appeal in August 2005 did not reject the guilty verdict, but his fine was reduced to £75,000. Chelsea were also fined £300,000 and Mourinho was fined £200,000, reduced on appeal in August 2005 to £75,000.

Cole signed a one year extension to his contract on 18 July 2005, but a year later departed from the club in acrimonious circumstances. On 15 July 2006, Cole launched a verbal attack on Arsenal; in his autobiography, quoted in The Sun, Cole claimed that the Arsenal board had treated him as a "scapegoat" and that they had "fed him to the sharks" over the tapping up affair. Cole was deliberately left out of Arsenal's 2006-07 team photograph, refuelling press speculation that he would become a Chelsea player.

On 28 July, Arsenal vice-chairman David Dein had confirmed that Arsenal and Chelsea had been in "civil talks" about the player. Chelsea insisted they would not raise their £16million bid for the left back, but Arsenal held out for at a higher valuation of £25m. Negotiations continued throughout August and looked to be heading for deadlock, but eventually Cole signed for Chelsea on August 31 for a fee of £5million, with William Gallas also going the other way. The deal was closed after the transfer window had officially ended, and was not confirmed until an hour and a half after the deadline had passed

Cole was given the number 3 shirt at Chelsea, and made his first appearance for the club as a substitute for Wayne Bridge in their 2-1 win over Charlton Athletic on 9 September. He also issued a public statement saying he forgave Arsenal for how he felt he was treated during his time there. On October 18, in a UEFA Champions League group A match against Barcelona at home, he crossed the ball low towards Didier Drogba at knee level, whom, after initially miss-controlling, scored the only goal of the game. Cole also generally had an impressive game and kept Barcelona's Lionel Messi quiet throughout.

--Wikipedia