It is always one of the more eagerly-anticipated fixtures of any Premier League season, and the meeting of Arsenal and Chelsea will again get pulses racing on Wednesday.
The London duo might be feeling pretty differently about themselves at the moment - with Arsenal struggling to keep pace with a top four which Chelsea have been a part of all season - but that won't make the meeting any less special nor the rivalry less fierce.
And one of the reasons behind that rivalry is the number of players who've swapped sides over the years.
No less than eight have done that during the Premier League era (that's post-1992, modern football fans) but who did it best?
Taking only their careers at both clubs into account, let's get ranking.
8. Lassana Diarra
A man who packed an awful lot into a relatively short period of time, the French midfielder was playing for Real Madrid just over three years after making his Chelsea debut at the age of 20.
He fitted in moves to Arsenal and Portsmouth in between that too, but he's barely remembered at the Emirates after playing just 13 times for the Gunners.
He was at least part of the Chelsea side that won the League and FA Cups in 2007, playing in the first game, so he gets some extra points for that.
And now he's being linked with PSG.
Chelsea career: 3/10
Arsenal career: 1/10
Total: 4/20
7. Yossi Benayoun
We know, we can hear you.
The Israeli midfielder is remembered much more for his (far better) stints and West Ham and Liverpool than for anything he did at Chelsea or Arsenal, but nonetheless those were his clubs between 2010 and 2012.
After leaving Anfield for Stamford Bridge he found opportunities hard to come by, and left on a season-long loan to Arsenal in August 2011, during which he'd play one more game (25) than he did during the three seasons he was a Chelsea player.
He managed to score six goals for the Gunners though, so that gives them the edge.
Chelsea career: 3/10
Arsenal career: 4/10
Total: 7/20
6. William Gallas
At a time when Chelsea were still paying sensible transfer fees for players, French defender Gallas arrived from Marseille for £6.2m in 2001, and proved to be a fine addition as he quickly struck up a fine partnership with a young John Terry.
Eventually, Jose Mourinho's arrival - and with him, Ricardo Carvalho - meant that Gallas was often shifted out to left-back, and his frustration over that eventually led to a move to Arsenal as part of a high-profile deal for Ashley Cole.
He went on to captain the Gunners, but his four years at the club were trophyless, and defined by a lack of both discipline and composure.
Chelsea career: 7/10
Arsenal career: 6/10
Total: 13/20
5. Emmanuel Petit
After arriving from Monaco in 1997, stylish French midfielder Petit would, in many ways, go on to symbolise this new Arsenal era under Arsene Wenger. He even appeared in an episode of The Bill in 1998 (he also won the Premier League and FA Cup double, and scored in the World Cup final as France beat Brazil 3-0, too).
That all led to a move to Barcelona, but after just one year there he was back in London with Chelsea in 2001, although his three years after the club failed to hit the heights of his time at Arsenal.
Arsenal career: 8/10
Chelsea career: 6/10
Total: 14/20
4. Nicolas Anelka
After Wenger poached him from Paris Saint-Germain as a teenager, Anelka had an impressive impact on his compatriot's Gunners team.
His goals helped Wenger's men to the league and cup double in 1998, before a 19-goal 1998/99 season attracted the interest of Real Madrid and kicked off a career of globetrotting around the football world.
Nine years after he left London he came back to sign for Chelsea in January 2008, and although he started slowly, his 19 Premier League goals helped the Blues to the league and cup double the following season.
Arsenal career: 7/10
Chelsea career: 8/10
Total: 15/20
3. Petr Cech
The dependable goalkeeper was signed before Jose Mourinho arrived at Stamford Bridge in the summer of 2004, but the Portuguese boss certainly was grateful to have him.
The Czech played for the Blues for 11 years, winning four league titles, four FA Cups and and the Champions League in 2012, with only Thibaut Courtois' emergence seeing him moved on in 2015.
That's when he joined the Gunners, and although age has withered his abilities somewhat, he's still one of the better goalkeepers in the Premier League.
Chelsea career: 9/10
Arsenal career: 7/10
Total: 16/20
2. Cesc Fabregas
Signed from Barcelona as a precocious youngster with a fantastic mullet, Fabregas eventually forced his way into the Arsenal midfield and left no-one in any doubt about his quality.
He eventually captained the side, but with trophy success at a premium in North London around this time, he moved back to Barca in 2011.
Three years later plenty wanted Arsenal to sign him back, but he opted to join Chelsea and has been rewarded with two league titles.
Arsenal career: 9/10
Chelsea career: 8/10
Total: 17/20
1. Ashley Cole
But if you think of Arsenal and Chelsea in the Premier League era, you inevitably think of Ashley Cole.
The left-back came through the ranks at the Gunners and was arguably the best player in his position in Europe for a while, nailing down a place in the England team and winning two Premier League titles and three FA Cups.
A bitter contract row led to him joining Chelsea in 2006, and in eight seasons at Stamford Bridge he managed to lift the Premier League, four FA Cups and the Champions League.
That's quite the medal collection, making him our No. 1.
Arsenal career: 9/10
Chelsea career: 9/10