Following six months of intense continental competition the protagonists have been whittled down to just four teams in both the Champions and Challenge Cups.
ESPN's experts predict which sides are set for a big weekend, which players will shine and where your attention should be trained across the semifinal action.
Player to watch
Champions Cup (Martyn Thomas): Tadhg Beirne (Scarlets). The former Leinster academy product returns to Dublin this weekend hoping to heap more misery on his old province. Beirne put in a supreme shift at the RDS Arena last May as 14-man Scarlets beat Leinster in the PRO12 playoff semifinals, making all 15 of his attempted tackles. His former teammate Dan Leavy revealed the "straight-out brawls" that formed their early life at Leinster, and having signed a contract with Munster for next season, Beirne will have plenty of motivation at the Aviva Stadium.
Challenge Cup (James Harrington): Gethin Jenkins (Cardiff Blues). When most rugby players hit the age of 37, they are either about to retire or have already done so. But prop from another planet Jenkins has other ideas. Just last week, Wales's most-capped player signed a one-year contract extension at the Blues. This Saturday, he could lead the PRO14 side to their second Challenge Cup final as Cardiff entertain Pau at the Arms Park. The sides have met twice before, and the hosts this weekend have won both times -- but the visitors have a perfect win record in the competition this season. Something will have to give.
Game of the weekend
Champions Cup: Leinster vs. Scarlets, Saturday, 3.30 p.m.
Leinster, the only unbeaten side in this year's Champions Cup, host the team that knocked them out on home soil in a domestic semifinal last season. The Scarlets' propensity for running rugby is well documented, but the free-scoring side from west Wales -- who disposed of La Rochelle in the last eight -- will come up against the tournament favourites in Dublin. Leinster were frighteningly good for large spells of their quarterfinal win over Saracens at the Aviva Stadium as the youth of James Ryan, Dan Leavy and Garry Ringrose gelled with the experience of Johnny Sexton, Rob Kearney and Isa Nacewa. Back on familiar ground, they will fancy their chances again.
Challenge Cup: Gloucester vs. Newcastle, Friday, 7.45 p.m.
The Premiership's sixth-placed side entertain fourth-placed rivals for the first time in the semifinals of a major European competition. Honestly, there is nothing to hate and everything to love about this fixture between the two most free-scoring sides in the Challenge Cup. But, interestingly, in their two Premiership meetings this season, the away side has taken the spoils. The Falcons, who have lost all four of their Challenge Cup semifinals to date, will want that seasonal quirk to hold for one more match -- and no English side loves a match under the Friday night lights more than Newcastle.
Champions Cup: Munster. It will undoubtedly be an emotional occasion for the Irish province as they return to France to face Racing 92 -- the team they were preparing to play when Axel Foley passed away suddenly in October 2016. The two sides met in the group stages, and shared a narrow victory apiece as Munster topped Pool 4. Were it not for a moment of magic from Andrew Conway, following an errant kick from Francois Trinh-Duc, Munster would not have emerged from their quarterfinal clash with Toulon. A former player, Donnacha Ryan, and the majestic Dan Carter stand between them and the Bilbao showpiece -- but Munster won't lack for belief in Bordeaux.
Challenge Cup: Newcastle. Dean Richards' Falcons have been a joy to watch all season. And they look to have a hankering for the Challenge Cup. Newcastle and Pau are the only two undefeated sides in the tournament -- and the former have Adam Radwan on their books. He has already equalled Tom Varndell's record of 10 touchdowns in a tournament, and it would be a brave punter who bets against him adding to that tally. The odds may be very much against it as both sides are away from home, but a Newcastle-Pau final would be something to behold.
Big weekend for...
Champions Cup: Dan Carter. The All Black great leaves Racing 92 for the Kobelco Steelers in Japan at the end of the season, and will want to board the plane with a European medal draped around his neck. Carter admitted this week that the thought of making history with Racing, who have never won a European title, is a driving factor for him as he prepares to pack his bags after three years in Paris. Carter led the Parisians to the final in 2016, where they were beaten by Saracens, and proved he can still turn a game as he came off the bench to inspire his side past Clermont in the quarterfinals.
Challenge Cup: Pau. A surprising Top 14 defeat at home to Agen at the weekend has put the entire season on a knife-edge for the Challenge Cup's last French side standing. Suddenly, with just two matches of the domestic season left, they are out of the end-of-season playoff places. Given their brief run-in includes a trip to Montpellier's Fortress Altrad and a home match against Toulon -- who could still be in the running for second and a bye to the semifinals -- this tournament has suddenly become their best chance for a Champions Cup place next season.