How they got here Dortmund won four games and lost two to finish top of a tough Group F that included Arsenal. The Germans then beat Zenit St. Petersburg 5-4 on aggregate, doing the damage with a 4-2 first-leg win in Russia.
Past meetings W3 D1 L2. United lost an agonising Champions League semi-final to the eventual winners in 1997.
Sub-plot A tie against Dortmund would pit Shinji Kagawa against his former club, with whom he won two league titles.
Star man Rangy frontman Robert Lewandowski, who'll join Bayern Munich in the summer, has played in all eight European games this term, scoring six times.
How they got here Jose Mourinho’s men topped Group E before beating Galatasaray in the Last 16. A 1-1 draw in Turkey was followed by a 2-0 triumph at Stamford Bridge.
Past meetings W2 D1 L0. No United fan will ever forget the dramatic penalty shootout victory over the Blues in Moscow to clinch 2008’s trophy.
Sub-plot An all-English tie carries its own intricacies, but revenge against Mourinho after his Real Madrid side ended our hopes last season would be sweet.
Star man Eden Hazard is Chelsea’s top scorer this term and provides plenty of creativity going forward.
How they got here An emphatic 6-1 aggregate win over Bayer Leverkusen in the Last 16 was preceded by a similarly comfortable group-stage campaign. The French champions cruised to top spot in Group C.
Past meetings This would be the first meeting between the two clubs. United have, of course, met French opposition plenty of times, including Lille, Marseille and Lyon. Our record against French teams reads: W10 D6 L2.
Sub-plot PSG manager Laurent Blanc spent two seasons at Old Trafford and would receive a warm welcome from the fans.
Star man The mercurial Zlatan Ibrahimovic is the man to watch. The enigmatic Swede has 25 league goals to his name this season.
How they got here As if winning their group by nine points wasn't enough, Real spanked Schalke 9-2 on aggregate in the Last 16. Mind you, they've only kept clean sheets against FC Copenhagen so far, suggesting their defence isn’t exactly rock-solid.
Past meetings P10 W2 D4 L4. The Reds have met the nine-times European champions on 10 occasions, most recently over two legs last year.
Sub-plot The Reds will be out for revenge after last season's controversial exit, while there's also the mouth-watering prospect of another Cristiano Ronaldo reunion.
Star man Ronaldo has netted 13 goals in Europe this season... just two shy of