Ahead of Celtic v Rangers on Saturday, we look at the history of the Old Firm, the best stats and players to watch out for...
For the first time in half a decade, the Scottish Premiership has a familiar look to it. Top of the table are Celtic with Rangers hot on their heels after four years spent in Scottish football's lower divisions.
And it means the scene is perfectly set for the most anticipated Old Firm match in decades, one of the most fiercely fought rivalries in football.
The last league meeting between these was in 2012, when Celtic cruised to a 3-0 win at Parkhead en-route to their first of five consecutive Scottish titles.
But it was Rangers who created the bigger waves that season, dropping into a financial spiral that saw the club liquidated and then reformed in the fourth tier of the league pyramid.
Plenty has changed since that 2012 meeting, but we have it covered right here, including the players to watch, the form of the two teams, and why this fixture matters quite so much...
Players to watch
Celtic: Scott Sinclair
Celtic could be the perfect destination for Sinclair to rejuvenate a career that had threatened to fizzle out. The former Chelsea, Swansea, Manchester City and Aston Villa forward has scored four goals in six appearances for the Hoops, including one on his debut.
Celtic: Leigh Griffiths
The danger man as far as Rangers are concerned. Celtic's No 9 is expected to be fit after missing out on Scotland's 5-1 win over Malta at the weekend, which is huge for Hoops boss Brendan Rodgers.
Griffiths, who hit 31 league goals last season, already has two in his first three league appearances.
Celtic: Tom Rogic
The Australian midfielder has been superb for Celtic since returning from the A-League. He recently signed a new long-term contract amid reported interest from Premier League clubs and it's not hard to see why.
It will be up to Rogic to set the tempo for Rodgers' midfield if they are to dominate proceedings on Saturday.
Rangers: Joey Barton
Rangers' biggest summer signing needs little introduction.
Barton will relish the occasion, which could well be a positive but may also leave him vulnerable to an early bath.
There must also be concerns over the capability of Barton's 34-year-old legs to deal with the pace and intensity of the fixture. With time on the ball, he should be superb for Rangers this season, but he's not going to get that platform on Saturday.
If he hits his stride then Barton's passing range could be a big factor in the game, but Celtic will look to get under his skin.
Rangers: Niko Kranjcar
There are few more talented footballers in the Scottish Premiership than Kranjcar, but even in his prime he was not known for his tenacity.
Add fitness concerns to a slightly lightweight style and it explains why Rangers are expected to have the Croatian on the bench for the fourth time this season.
His fluid and creative style of play could be exactly what Rangers need late in the game once slightly more space has opened up.
Rangers: Lee Wallace
Captains are always crucial figures in Old Firm games, and Rangers will be praying that Lee Wallace is fully fit after injury curtailed his time with the national squad.
At his best, Wallace leads by example, but if he's off his game then Celtic will look to expose him on the turn.
Managers
Rangers: Mark Warburton
There was a widespread shrugging of shoulders when Rangers appointed Warburton in June 2015. The former Boreham Wood defender was hardly a glamorous name, with only two years of managerial experience at Brentford behind him.
But those in the know realised he was potentially an excellent appointment. A highly-regarded coach and sporting director, Warburton was also one of the people behind the NextGen Series, highlighting his interest in youth development.
Fast forward a year and Warburton has been an overwhelming success, steering the club to a league and cup double, falling just narrowly short of a treble with defeat to Hibernian in the Scottish Cup final.
Celtic: Brendan Rodgers
Rodgers' arrival was a huge coup for Celtic and garnered plenty of excitement among the fans, but the start of his tenure has not been smooth sailing.
A 1-0 defeat to Gibraltar's Lincoln Red Imps in his first game was extremely embarrassing - despite Rodgers' claims to the contrary - and a 5-4 aggregate win over Hapoel Be'er Sheva to seal a place in the Champions League group stage was far less convincing than it should have been.
Celtic have the best squad in the division and a manager capable of making them tick, but at this stage it's too early to say whether Rodgers and Celtic are going to click.
Opta stats
This is the first Old Firm clash in the league since April 2012, when Celtic won 3-0 at Celtic Park. However, Rangers came out on top in their last competitive meeting in April, winning 5-4 on penalties after a 2-2 draw to reach the Scottish Cup final.
Rangers have failed to score on their last three league visits to Celtic Park, losing all three and conceding seven goals.
Kris Commons has scored two goals in his four Scottish Premiership Old Firm games, including the second goal in Celtic's 3-0 win the last time they met in league competition.
Commons and Griffiths were on target the last time Celtic defeated Rangers - in a 2-0 League Cup semi-final victory at Hampden Park in February 2015.
In each of the last five Scottish Premiership seasons these sides have faced each other, Rangers have won the first clash of the campaign (2007/08 to 2011/12).
Kenny Miller has scored seven goals in his last nine Old Firm clashes for Rangers (league only), netting three braces along the way.
The Hoops have won each of their last four Scottish Premiership clashes, scoring 17 goals (4.3 goals per game).
Rangers are unbeaten in their first four games back in the Scottish Premiership since 2012 (W2 D2); the only other remaining side yet to lose is Celtic.
Sinclair has scored in his first three successive league games for Celtic - he hasn't scored four in a row in the league since October 2010.
Players who crossed the divide
Only five players have crossed the River Clyde divide since the end of the Second World War, but one of those is set to play this weekend.
Rangers forward Kenny Miller has started all four of his club's league matches so far this season and will expect to be picked for Saturday's big game.
Not content with crossing the Clyde once, Miller has actually done it twice - making him one of just two players in history to have done so (the other is Tom Dunbar, who played his final game way back in 1897).
One season at Rangers in 2000-01 was enough to earn Miller a move south of the border to Wolves, but he returned six years later to sign for Celtic.
He then left Parkhead after just a year to join Derby, before moving back the following season…to rejoin Rangers. Following stints in Turkey, Wales and MLS, he returned to Ibrox for a third time in 2014.
How did the Old Firm come about?
Sky Sports sat down with Scottish Football history museum curator Richard McBrearty to find out...
"It goes back to the very late 19th century in Scotland," McBrearty said. "The game had turned professional by 1893, league football had been created by 1890 and the game started to really transform from an amateur game.
"From the turn of the century you have these two clubs - Celtic and Rangers - starting to regularly play each other in major cup finals and so because they are constantly making cup finals, they were making a lot of money.
"Football was almost seen as a business by that period and so they were referred to as a factor or a firm. And so because of always getting to finals, they were referred to as the Old Firm.
"It's a term about the financial success of both clubs, competing at the top end of Scottish football and making lots of money off the back of it."
Recent classics
Celtic 6-2 Rangers - August, 2000
It was a dream Old Firm debut for Martin O'Neill as his Celtic side ran riot.
Chris Sutton and Henrik Larsson grabbed two goals each, while Stiliyan Petrov and Paul Lambert also netted for the home side.
Claudio Reyna and Billy Dodds added a degree of respectability to the scoreline from Rangers' point of view, but this was undoubtedly a day for Celtic fans.
Rangers 4-2 Celtic - September, 2011
A Charlie Mulgrew red card, a Steven Naismith brace and a Rangers come-from-behind victory all mixed together to form a topsy-turvy six-goal thriller. This breathless encounter at Ibrox was the perfect start to the 2011/12 season.
The campaign ended with Celtic as champions and Rangers liquidated, but on this September day, Gers fans went home the happier.
Celtic 2-2 Rangers AET (4-5 on penalties) - April, 2016
A classic from last season, when then-Championship side Rangers beat their old rivals in the Scottish Cup semi-final thanks to a dramatic penalty shoot-out.
The game had just about everything, including a stunning long-range strike, a couple of near misses, and plenty of end-to-end action, leaving both sets of players out on their feet at the final whistle.
Rogic, whose extra-time goal had taken the game to penalties, missed the decisive spot-kick for Ronny Deila's side after the match had earlier finished 2-2.