This article documents the history of Chelsea Football Club, an English association football team based in Fulham, West London. For a general overview of the club, see Chelsea F.C.

In 2003, Chelsea were bought by Russian billionaire Roman Abramovich, ushering in an era of substantial success. José Mourinho led them to two league titles, an FA Cup and two League Cups in three seasons. The club added a further FA Cup in 2009, and then their first League and FA Cup "Double" in 2010. Under the stewardship of former player Roberto Di Matteo, the club won a seventh FA Cup in 2012, before winning their first UEFA Champions League title. Followed by their first UEFA Europa League victory a year after. Further Premier League victories followed in 2015 and 2017. They won their 8th FA Cup in 2018 and a second Europa League in 2019. This was followed by a second UEFA Champions League victory in 2021. In March 2022, Chelsea was seized from Abramovich after sanctions imposed by the British government. On 30 May 2022, the £4.25 billion Todd Boehly-led consortium announced completion of the ownership transfer of Chelsea, ending Abramovich's 19 year ownership of the club.

2003: start of Abramovich Era With the club facing an apparent financial crisis,Chelsea saviour arrived in time for £23 m bill . URL accessed on 11 April 2006. Bates unexpectedly sold Chelsea F.C. in June 2003 for £60 million.Bates sells off Chelsea to a Russian billionaire . URL accessed on 20 April 2014. In so doing, he reportedly recognised a personal profit of £17 million on the club he had bought for £1 in 1982 (his stake had been diluted to just below 30% over the years). The club's new owner was Russian oligarch and billionaire Roman Abramovich, who also took on responsibility for the club's debt, in the region of £80 million, quickly paying some of it. He then went on a £100 million spending spree before the start of the season and landed players like Claude Makélélé, Geremi, Hernán Crespo, Wayne Bridge, Glen Johnson, Joe Cole and Damien Duff.

The spending saw a good return, with Chelsea finishing as Premier League runners-up (their best league finish for 49 years) and reaching the Champions League semi-finals after dramatically beating the Arsenal Invincibles in the quarter-finals. However, Chelsea lost the semi-final to Monaco; with manager Claudio Ranieri criticised for some tactical decisions such as switching central midfielder Scott Parker to right-back and right-back Glen Johnson to centre-back to accommodate more attackers in the team. Ranieri was eventually sacked and replaced by José Mourinho (who had lifted two Portuguese league titles, a Portuguese Cup, a Champions League title and a UEFA Cup with Porto) as the club's new manager.

José Mourinho: double League Champions (2004–07)

2004–05 was a successful season despite a slow start to the league season, trailing leaders Arsenal by five points. Chelsea's title campaign gradually picked up momentum, driven by the high-scoring Frank Lampard and the return from injury of talented young Dutch winger Arjen Robben. They topped the table after a win against Everton in November 2004 and never relinquished their lead, losing only one league game all season and winning a record 29, gaining a record 95 points in the process. A record-breaking defence, led by captain John Terry and his new partnership with Ricardo Carvalho, the versatile William Gallas, fullback Paulo Ferreira, midfield linchpin Claude Makélélé and goalkeeper Petr Čech, provided the backbone of the side, conceding just 15 goals all season and keeping 25 clean sheets while Čech went a Premier League-record 1,025 minutes without conceding a goal. Chelsea eventually secured the title with a 2–0 away win at Bolton thanks to two goals from Lampard, almost 50 years to the day since they had won their last league title. Winning the league completed a domestic double for the club, since Chelsea had already won the League Cup in February after a thrilling 3–2 win over Liverpool in the Final at the Millennium Stadium.

In the Champions League, Chelsea were drawn against Barcelona in the knockout round. In the first leg at the Camp Nou, Chelsea took a 1–0 lead but had Didier Drogba controversially sent-off in the second half with Chelsea still ahead, and the Catalans eventually won 2–1. Mourinho claimed that Barcelona manager Frank Rijkaard had spoken to referee Anders Frisk at half-time – a claim later proved correct – and that the result had been "adulterated". After receiving death threats from Chelsea fans, Frisk retired and Mourinho received a two-match touchline ban for bringing the game into disrepute. Chelsea won a pulsating return leg 4–2 at Stamford Bridge, with John Terry heading in a controversial winner to send them through. In the quarter-finals, a 4–2 home win over German champions Bayern Munich and a 3–2 loss in Germany were enough to ensure passage through to the semi-finals, where they faced Liverpool. Following a 0–0 draw at Stamford Bridge, Liverpool went 1–0 up at Anfield thanks to Luis García and Chelsea were unable to break down a resilient defence, thus missing out on the chance of a treble.

A year later Chelsea retained their league title, signing Shaun Wright-Phillips in the summer for £21 million and setting more records in the process. Winning their first nine games, the side emphatically set the pace in the Premier League – including a 4–1 win over Liverpool at Anfield – and at one stage were 18 points ahead of nearest rivals Manchester United. Following a late-season blip, and with United on a run of nine consecutive wins, the points gap was closed to seven points as Chelsea went into a key match with West Ham. A goal down after ten minutes and a man down after 17 following Maniche's sending off, the side bounced back to win 4–1 and maintain the gap. The title was eventually secured with a 3–0 win over United at Stamford Bridge. They became the first London club to win back-to-back league titles since the 1930s, and only the fifth side to do so since the Second World War. They also set the record for the most clean sheets (six) from the start of the season and equalled the best home record for a top division team since Newcastle United in 1906–07 (18 wins and 1 draw from 19 games). In the cups, however, there was less success as they were knocked out of the Champions League by Barcelona and the FA Cup semi-final by Liverpool.

Despite the arrival of Ashley Cole, Michael Ballack and Andriy Shevchenko the 2006–07 season saw Chelsea relinquish the Premier League trophy to Manchester United after remaining second in the league for the majority of the season. The club were still in the running to achieve an unprecedented quadruple at the end of April, and played all but one of the maximum 63 possible games at the start of the season. They won the League Cup by beating Arsenal 2–1 in the last ever English cup Final at the Millennium Stadium, and beat United 1–0 in the first FA Cup Final at the new Wembley Stadium; Chelsea were also the last team to win it at the old Wembley. They reached the semi-finals of the Champions League, only to be knocked out again by Liverpool, this time in a penalty shoot-out.

Post Mourinho Era (2007–09) On 20 September 2007, Mourinho left Chelsea by "mutual consent" following an indifferent start to the season and after several months of well-documented friction between Mourinho and Abramovich. Shortly afterwards, Israeli Avram Grant, who had been appointed Chelsea's director of football on 8 July 2007, was announced as Mourinho's successor.

Despite the managerial upheaval and a high level of player absence (in all, members of the team were unavailable for selection 286 times in the 62 fixtures), Chelsea were on course to win three different competitions, a feat previously achieved by only two other English clubs, Liverpool in 1983–84 and Manchester United in 1998–99, but ultimately finished as runners-up in all three. Chelsea reached their third League Cup final in four years, but suffered a surprise 2–1 defeat to mid-table Tottenham at Wembley. Chelsea emerged as United's closest rivals in the title race; a 2–1 victory over United at Stamford Bridge in April left the teams level on points with four games remaining. The teams were still level on points going into the final game of the season, although United's superior goal difference meant Chelsea had to better their result; in the event, Chelsea drew 1–1 with Bolton Wanderers and United beat Wigan Athletic to take the title.

Grant also led Chelsea to their fourth Champions League semi-final in five years, and they were again drawn to face Liverpool, although this time it was Chelsea who prevailed, winning 4–3 on aggregate to reach the Final for the first time in their history. Their opponents in the Final were Manchester United, making it the first all-English final in the competition's history. In an even game, Lampard's first-half strike cancelled out Cristiano Ronaldo's opener, and the teams remained at 1–1 for the rest of the match, taking the final to a penalty shootout, where John Terry and Nicolas Anelka's misses from the spot gave United victory.

After the conclusion of the 2007–08 season, Chelsea became the highest ranked club under UEFA's five-year coefficient system used in the seeding of European club competitions in the following season, a sign of the consistency of the club's performance over the first five years of Roman Abramovich's ownership.

Grant was sacked as Chelsea manager three days later. Grant's replacement was Brazilian Luiz Felipe Scolari, who had guided Brazil to victory at the 2002 World Cup and Portugal to runners-up at UEFA Euro 2004. However, despite a bright start which saw Chelsea top the Premier League table early in the season, Scolari was sacked on 9 February 2009 due to "results and performances of the team... deteriorating at a key time in the season", and with the club lying fourth in the Premier League. Russia national team coach Guus Hiddink was appointed caretaker manager until the end of the season. Under Hiddink, performances and results improved; Chelsea lost just one more game all season, eventually finishing third in the league and reaching the FA Cup Final.

In the Champions League, a 7–5 aggregate win over Liverpool in the quarter-finals, including an epic 4–4 draw at Stamford Bridge, took Chelsea to another semi-final, against Barcelona. After drawing 0–0 in the first leg at the Camp Nou, Chelsea took an early lead in the second through Michael Essien, but in a controversial game in which Chelsea squandered numerous chances and had several penalty appeals turned down, a stoppage time equaliser from Andrés Iniesta sent Barcelona through on away goals. In the immediate aftermath, Drogba caused more controversy after swearing at referee Tom Henning Øvrebø. In consolation, goals from Drogba and Lampard gave Chelsea a 2–1 victory over Everton in the FA Cup Final at Wembley on 30 May, the club's second FA Cup triumph in three years.

The Ancelotti era (2009–11)

Former Milan coach Carlo Ancelotti was confirmed as Hiddink's successor on 1 June 2009. He started his career by winning the World Football Challenge, played in the United States. In Ancelotti's first competitive match, Chelsea met Manchester United in the Community Shield. The game ended in a 2–2 draw, with Chelsea winning 4–1 on penalties to take the trophy, the club's first victory in a shoot-out since beating Ipswich Town in the League Cup in January 1998.