True head-to-head title battles between both clubs have been rare despite being England's most successful sides
It's viewed in some quarters as a kind of English Clasico.
And certainly the Manchester United-Liverpool rivalry has many elements which match up to the all-time great rivalries across the globe from Barca-Real to Boca-River and Juventus-Inter.
From the geographic proximity of the two large cities in the northern half of England to being the two most successful clubs in the Football League based on trophies and European achievements, plenty unites as well as divides them.
The duo also were the first two English clubs to win the old European Cup with United doing so in 1968 and Liverpool kickstarting an era of success on the continent with a first triumph in 1977.
Europe is a key part of the aura and history of both sides and that is evident in the build up to their clash tonight at Anfield in the lesser Europa League.
But the rivalry is odd in another way in comparison to rivalries like El Clasico or others in Portugal and the Netherlands in particular where head-to-head races between the top two or three are the norm.
As strong as it is, a truly direct title battle between Liverpool and Man United has been quite rare during their long histories together over the last 40 years.
Joe Jordan (extreme right) turns away in triumph after equalising for Manchester United in the 20th minute of this afternoon's FA Cup semi-final against Liverpool at Maine road. Picture by: PA / PA Archive/Press Association Images
Indeed, their status as diminished upper mid-table clubs might be similar at the moment, but the last time they fought for a title was the 2008-09 season when United battled back to prevent Rafa Benitez's Liverpool from taking a first Premier League title since 1990 with the Spaniard's "facts" rant among the highlights of that tete a tete.
That 26 year gap has featured much success for United but the vast majority of that time, the Alex Ferguson teams of old had to contend with Blackburn, Newcastle, Arsenal, Chelsea and Manchester City as the truly direct rival.
And in the pre-Fergie era when Liverpool were at their peak, United were further behind as the likes of Everton and Arsenal took up the challenger mantle. United did finish second to Liverpool in 1987-88 under Fergie, but they marooned in that runner-up spot as they were nine points back at the end of the season and eight points clear of third-placed Nottingham Forest.
However, if you go back all the way to 1979-80, Liverpool pipped United to the First Division title by a whisker with two points separating them.
Both teams lost their final games that season, with United having closed the gap in the final run-in with six wins in a row, kickstarted by a 2-1 victory at home to Liverpool.
However, the Merseysiders' goal difference was vastly superior as they held on for their 12 league crown. Of course their later mark of 18 has now been superseded by their great rivals' 20. But unfortunately that has rarely been achieved in direct battles to the finish line.