Scarlets hooker Ken Owens believes it's win or bust for his side as they bid to get their European campaign back on track this weekend.
Four teams contested the 2011 Play-Offs, with Munster looking to defend their title against Ospreys, while Leinster met Glasgow in the other knockout game.
In a repeat of the 2010 final, Leinster met Ospreys at the RDS, in what turned out to be a thrilling encounter, decided by a last-minute Dan Biggar conversion.
Munster took the 2011 title in their back yard of Thomond Park
The 2011 Final was contested between Munster and Leinster.
The Ospreys took the 2010 title
Leinster, who finished first at the end of the regular league season, beat Munster, who finished fourth, while the Ospreys backed up their second-place finish with a win over the third-place Warriors at the Play-Off stage.
That set up a mouthwatering Final between the league's two most consistent teams in front of a packed house at the RDS on May 29, 2010.
Tries from Tommy Bowe and Lee Byrne, together with two conversions and a penalty from Dan Biggar, secured Final glory for the Ospreys with a 17-12 victory in the Irish capital.
Match records: team
Most Points 31 Ospreys (2012)
Least Points 9 Leinster (2010)
Biggest Win Margin 10 Munster (2011)
Smallest Win Margin 1 Ospreys (2012)
Highest Points Aggregate 61 (2012)
Most Points Half-Time 17 Leinster (2012)
Least Points Half-Time 3 Leinster (2010)
Most Tries 3 Ospreys (2012) and Leinster (2012)
Most Cons 3 Leinster (2012)
Most Pens 4 Leinster (2010)
Fastest Try 12min Doug Howlett (Munster, 2011)
Latest Try 79min Penalty Try (Munster, 2011)
Latest Scorer 80min Ronan O'Gara (Munster, 2011)
Most Points 36 Jonathan Sexton (Leinster, 2010,2011 and 2012)
Most Tries 2, Isa Nacewa (Leinster) and Shane Williams (Ospreys), both 2012
Most Cons 4 Dan Biggar (Ospreys, 2010 and 2012)
Most Pens 10 Jonathan Sexton (Leinster, 2010, 2011 and 2012)
In the first few years of its existence, the Celtic League winners were determined via a Play-Off programme.
The Celtic League began life on August 17, 2001, when 15 teams from Wales (9), Ireland (4) and Scotland (2), split into two pools playing each other just once. The top four teams from each pool qualified for the knockout quarter-finals in late November, with the semi-finals taking place early in December. The inaugural final was then staged at Lansdowne Road on 15 December 2001, where 30,000 fans saw Leinster defeat Munster 24-20.
30/11/2001 Ulster 38 - 29 Neath
30/11/2001 Leinster 34 - 22 Newport
01/12/2001 Connacht 29 - 34 Glasgow
01/12/2001 Munster 13 - 6 Llanelli
07/12/2001 Leinster 35 - 13 Glasgow
08/12/2001 Munster 15 - 9 Ulster
15/12/2001 Leinster 24 - 20 Munster (Lansdowne Road)
Leinster celebrate their 2001 success over Munster
The Celtic League expanded to 16 teams with the introduction of a third Scottish side - the Borders - in 2002/03, but the teams still only met once during the season. A bonus-point scheme was introduced and the quarter-finals were staged in November and the semi-finals in January.
The second Celtic League Final took place at the Millennium Stadium on February 1, 2003, and Munster made up for their disappointment at losing the previous year in Dublin by beating Neath 37-17 in front of more than 30,000 fans.
29/11/2002 Pontypridd 12 - 13 Neath
29/11/2002 Munster 33 - 3 Connacht
30/11/2002 Glasgow 17 - 20 Ulster
30/11/2002 Edinburgh 22 - 26 Cardiff Rugby
03/01/2003 Munster 42 - 10 Ulster
04/01/2003 Neath 32 - 10 Cardiff Rugby
01/02/2003 Munster 37 - 17 Neath (Millennium Stadium)
From 2004 to 2009, the league reverted back to deciding it's champions by a traditional league format. That all changed again in 2010 and the success of the new system looks set to ensure the Final remains the focal point of the RaboDirect PRO12 season for years to come.
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