The Magners League will be a 12-team competition from next season after Celtic Rugby today confirmed two Italian teams will start the season next year.
Benetton Treviso and Aironi Rugby will join the league for the 2010/11 season after the three Celtic Unions unanimously agreed to ratify their inclusion.
The decision ends a year-long study into the viability of expanding the competition.
“Benetton Treviso will have their headquarters at Stadio Comunale di Monigo while Aironi, who will be based at Stadio Luigi Zaffanella, will involve various clubs from the Lombardia and Emilia-Romagna regions,” a statement read this afternoon.
Director of Celtic Rugby, David Jordan said: "This is another massive step forward for the Magners League and follows the decision to go to a top four play-off system to determine our champion team.
"As well as providing more fixtures for the teams already involved this will also bring both a major cash injection into the competition and greater exposure across Europe.
"The implementation of the plays-offs and the Magners League Grand Final this season has already seen a marked improvement in the competitiveness of the League and the arrival of two Italian teams will provide another boost to the competition.
"Operationally it will present new challenges, as well as opportunities, but by introducing Italy into the Celtic fold it will also dramatically broaden the appeal of our product.
"It is anticipated that the Italian super clubs will be largely made up of Italian internationals of full, A and under 20 levels, with a sprinkling of top class overseas players set to provide further extra strength and spice to the tournament."
President of Federazione Italiana Rugby (FIR), Giancarlo Dondi said: "I am very pleased that, after months of intense negotiations, an agreement that will see two Italian teams join the Magners League at the start of next season has been reached.
"I would like to thank the Board of Celtic Rugby, in particular president John Hussey and director David Jordan, for the support given in recent months.
He added: "I am sure that the Magners League will bring benefits to all Italian rugby and will have a positive impact on the competitiveness of our national team."
The IRFU has also welcomed the move this afternoon. In a statement, chief executive Philip Browne said: "The inclusion of the two Italian sides for next season can only strengthen the competition into the future.
"The Magners League has continually grown year on year in terms of attendances, viewership and standards during its lifetime and the news today certainly continues this progression."
"Ultimately what is good for the Magners League will be good for European rugby and also for the international game by bringing Italian rugby into the competition".