The Ospreys will be chasing a third title in four years when the RaboDirect PRO12 season kicks off this weekend.
The Liberty Stadium outfit have quickly become the masters of the play-off system in the Celtic League - and they will be the side to beat once again despite the large departure of players in the summer.
Heineken Cup champions Leinster, beaten in the past two finals, will once again lead the charge from Ireland, while Munster will hope new coach Rob Penney can revive their fortunes.
The Scarlets, Cardiff Blues, Glasgow and Ulster will also have new men at the helm for their 2012/13 challenge, while Zebre have replaced Aironi as Italy's second team.
Aironi were disbanded after issues on and off the pitch, however, Treviso have proved that there is a place in the competition for the Italian teams.
Connacht and the Dragons will be out to avoid a fight at the bottom of the table, while Edinburgh will want to carry across their Heineken Cup form into the domestic competition.
The Blues endured a disappointing season by their standards and have turned to former Leeds and Scarlets boss Phil Davies in a bid to lead them forward.
It will not be an easy task, though, with the Blues having had to drastically trim their playing budget - with the likes of Gethin Jenkins, John Yapp, Richie Rees, Casey Laulala, Dan Parks and Ben Blair among those to leave. Deiniol Jones, Paul Tito, Ma'ama Molitika and Martyn Williams have also retired, leaving some pretty big boots to fill.
The Blues, though, have bolstered their pack with the likes of Campese Ma'afu, Andy Kyriacou, Benoît Bourrust and Lou Reed, while Rob Lewis and Jason Tovey could form an exciting half-back combination.
And with the likes of Jamie Roberts, Sam Warburton, Harry Robinson, Leigh Halfpenny and Alex Curthbert - as well as emerging talents Josh Navidi, Cory Allen and Luke Hamilton - to call upon, the Blues will be hoping to mount a serious challenge.
Key man: In Sam Warburton the club possess one of the leading back-rowers in the game - and the Blues will need him to maintain his impressive form.
While an eighth-place finish might not sound that impressive, for Connacht it was their best season since the Celtic League moved to a one-division format.
It was also the next step in the progression for Connacht under Eric Elwood, who has worked wonders with the weakest of the four Irish provinces.
The arrival of the free-scoring Dan Parks is an indication of the lure of the club, while Danie Poolman looks an exciting addition.
In Rodney Ah You, Mike McCarthy, Ronan Loughney, Brett Wilkinson, John Muldoon, Eoin Griffin and Fetu'u Vainikolo they have some class players - while Denis Buckley, Mick Kearney and Shane Layden are the latest to emerge from the club's academy.
Key man: Dan Parks remains a deadly kicker and his accuracy and experience could see Connacht continue their rise up the rankings.
While Edinburgh may have been enjoying their best-ever season in the Heineken Cup, their domestic form was hardly something to shout about.
Just six wins from 22 games meant they finished down in 11th - with only troubled outfit Aironi sparing them the embarrassment of coming last.
Michael Bradley, whose side was shorn of talent during the World Cup and international period, has moved to address the issues with a number of key additions - including Andy Titterrell, Richie Rees, John Yapp, Greig Tonks, Mike Penn and Ben Atiga - while Neil Back has joined as forwards coach.
And while Mike Blair, Chris Paterson and Phil Godman are among those to leave, Edinburgh still have the class act that is Tim Visser, along with Greig Laidlaw, Ross Rennie, David Denton and Lee Jones.
Key man: Tim Visser is the deadliest finisher in the ReboDirect PRO12 - with his form deservedly earning him a call-up to the Scotland team.
Having gate-crashed the play-offs last season, Glasgow will be looking to build on this platform under the guidance of Gregor Townsend.
The former Lions international has made the switch from the Scotland team to replace Sean Lineen at the helm - and he will be joined by a number of experienced campaigners.
Sean Lamont, Angus Macdonald, Viliami Ma'afu and Tim Swinson are among those to have signed, while Taylor Paris will look to make a big impact after impressing for Canada on the Sevens circuit.
Townsend can also rely on the likes of Alastair Kellock, Ruaridh Jackson, John Barclay and Rory Lamont - although Richie Gray, Johnnie Beattie and David Lemi are among those to have departed in the summer.
Key man: Former Scotland captain Alastair Kellock is a class operator and he can lead Glasgow's challenge for honours from the front.
They might be the kings of the Heineken Cup, however, the domestic title has proved a little harder for them to win - with three successive play-off final defeats.
The last of their two Celtic crowns came in 2008, but there is no doubting the talent within Josef Schmidt's squad.
In Brian O'Driscoll, Jonathan Sexton, Fergus McFadden, Sean O'Brien, Jamie Heaslip, Cian Healy and Rob Kearney they have some of Ireland's leading players.
Tom Denton, Michael Bent, Quinn Roux and Andrew Goodman have all arrived to bolster the squad, while the likes of Foster Horan, Tadhg Furlong, Tadhg Beirne, Jordan Coghlan and Jack Conan will be looking to make the step up from the academy - although Brad Thorn has left after his short spell at the club.
Key man: Sean O'Brien was the man of the match in the Heineken Cup final and he has the ability to guide Leinster to domestic honours when he returns to full fitness.
Rob Penney has been handed the responsibility of reviving Munster's challenge to become Ireland's - and Europe's - leading club.
The club did win the domestic crown in 2011 - with victory over Leinster - but they suffered a disappointing defeat to the Ospreys in the semi-finals last season.
They do have a hugely talented squad that includes Ronan O'Gara, Paul O'Connell, Peter Stringer and Donncha O'Callaghan, while James Downey, Casey Laulala and CJ Stander are the notable new arrivals. The club can also call upon the likes of highly-talented academy graduates JJ Hanrahan - one of the stars of the IRB Junior World Championships - and Sean Scanlon.
Munster have seen a number of departures, though, with Tomas O'Leary, Lifeimi Mafi, Denis Fogarty and Peter Borlase leaving and John Hayes, Mick O'Driscoll, Jerry Flannery, David Wallace, Denis Leamy and Darragh Hurley having been forced to retire.
Key man: JJ Hanrahan came of age at the IRB Junior World Championships - and looks to be the heir apparent to Ronan O'Gara's No.10 jersey.
The halcyons days when the Dragons finished third in the Celtic League back in 2004 must seem a lifetime ago for the club's fans.
The Dragons have promised so much over the years but have slipped well and truly down the pecking order of the Welsh regions.
Coach Darren Edwards and his squad finished in ninth last season - and the loss of the likes of Aled Brew, Martyn Thomas, Luke Charteris and Jason Tovey have left big voids to be filled.
However Tim Ryan, Tom Prydie, Ian Nimmo and Daniel Evans have all made the move to Rodney Parade ahead of the new campaign.
Key man: Following Luke Charteris' departure to France, Dan Lydiate can be the man to inspire the Dragons.
The Ospreys have adapted to the play-off system better than anyone in the Celtic League, with two titles and a semi-final appearance in the three years since its inception.
However, there has been a large exodus of players from the Liberty Stadium in the summer - and it is that loss of experience that could hamper their bid to defend their title.
Shane Williams, the match-winner in the final against Leinster, Huw Bennett, Tommy Bowe, Paul James, Chauncey O'Toole, Sonny Parker, Gareth Owen, Kristian Phillips, Nikki Walker and Barry Davies are among those that left.
Boss Steve Tandy has kept recruitment to a minimum - only James Goode and Jonathan Spratt have signed, while Tom Smith stays after initially agreeing to join London Irish.
But Tandy has an already talented squad, including the likes of Justin Tipuric, Dan Biggar, Alun Wyn Jones and Kahn Foruali'i, and an impressive academy section to call upon.Key man: Given the loss of experience at the Liberty Stadium the pressure will be on Alun Wyn Jones to lead by example.
Under the stewardship of Nigel Davies the Scarlets enjoyed a renaissance - but it will now be down to Simon Easterby to carry on the good work.
With Davies heading to Gloucester, former Ireland flanker Easterby makes the step up - and he inherits a talented squad full of young Welsh talent.
Rhys Priestland, Scott Williams, George North, Josh Turnbull, Liam Williams, Jonathan Davies and Matthew Rees are all class performers, while Adam Warren is the latest off the Parc y Scarlets production line.
However, Easterby has looked to bolstered his front five with the signings of George Earle, Jake Ball, Tomas Vallejos and Jacobie Adriaanse, while backs Gareth Owen and Kristian Phillips will get the chance to kick-start their careers.
Key man: Rhys Priestland has continued to grow into the No.10 jersey - but with no Stephen Jones to provide back-up, the Wales international will have the weight of expectation on his shoulders.
The Italians have adapted well since joining the league two seasons ago - finishing 10th on both occasions.
However, they will now be looking to climb the standings, especially given the number of Italian players within their ranks and their home form.
Tommaso Benvenuti, Edoardo Gori, Leonardo Ghiraldini, Robert Barbieri, Luke McLean and Alessandro Zanni are all talented performers.
And coach Franco Smith has bolstered the ranks with overseas experience in the shape of James Ambrosini, Dean Budd, Doppies La Grange, Christian Loamanu and Jacobus Roux.
Key man: Alessandro Zanni is a hard-tackling flanker and his defensive abilities will be tested to the limit.
Having reached the Heineken Cup final last season, there will be increased pressure for Ulster to perform domestically.
Former New Zealand Under-20s coach Mark Anscombe has arrived in the summer to take over the reins - and he will have a classy-looking squad to work with.
Roger Wilson and Tommy Bowe have both returned to join the likes of Ruan Pienaar, Rory Best, John Afoa, Stephen Ferris, Darren Cave and Andrew Trimble.
The club, though, have lost the services of the likes of Pedrie Wannenburg (Castres), Ian Humphreys (London Irish), Willie Faloon (Connacht), Simon Danielli (retiring), Stefan Terblanche (retiring) and Andy Kyriacou (Cardiff Blues).
Key man: Ruan Pienaar was the star of Ulster's charge towards the Heineken Cup final, with kicking second to none.
The league's new boys face a difficult challenge in the coming months, having replaced Aironi at the end of last season.
Roberto Manghi has been handed the responsibility of guiding the Zebras, while Vincenzo Troiani, Alessandro Troncon and Fabio Ongaro will provide crucial support.
A large selection of Aironi's squad have made the move across to the Stadio XXV Aprile - including Marco Bortolami, Quintin Geldenhuys, Salvatore Perugini, Tito Tebaldi, Matteo Pratichetti, Giovanbattista Venditti, Josh Sole and Mauro Bergamasco.
However, the club have pulled off a real coup with the signing of playmaker Daniel Halangahu from the Waratahs.
Key man: Zebre will be looking to Australian Daniel Halangahu to provide the creative spark in their debut season.