The 2015–16 Pro12 (also known as the Guinness Pro12 for sponsorship reasons) was the fifteenth season of the professional rugby union competition originally known as the Celtic League, and the sixth with its current four-country format.

Connacht – who qualified for the play-offs for the first time – then proceeded to defeat Leinster 20–10 in the final,[7][8] to become the seventh team to win the league title.

[16] D'Arcy had announced his intention to retire after the World Cup earlier in the year,[17] but ultimately didn't make the final Irish squad and played with Leinster until the conclusion of the tournament.

[18] Munster captain Peter O'Mahony missed the early season due to the World Cup, and suffered a serious injury in Ireland's game against France.

[19] The close season also saw the departure of long-serving players Donncha O'Callaghan and Paul O'Connell, both of whom had played for the province since before the league's foundation.

O'Callaghan, the province's record holder for appearances, was released from the final year of his contract to join newly promoted English Premiership side Worcester Warriors.

Over a year after the departures of David Humphreys and Mark Anscombe,[22] Les Kiss took over as Ulster Director of Rugby in October 2015.

[24] Benetton Treviso's captain Antonio Pavanello retired from playing at the end of the previous season, taking up a role as Sporting Director.

[37] Following the departure of Director of Rugby Mark Hammett in February 2015, for personal reasons,[38] Cardiff Blues appointed Danny Wilson their head coach ahead of the new season, replacing caretakers Dale McIntosh and Paul John.

[41][42] Newport Gwent Dragons captain Lee Byrne was forced to retire in April 2015 after he failed to recover from a shoulder injury.

[45] Both Scarlets captain Ken Owens and vice-captain Scott Williams went to the World Cup with Wales, missing the opening rounds of the league.

This match – originally scheduled to be held during Round 12, on 8 January 2016 – was postponed due to a European Rugby Champions Cup fixture rearrangement that occurred as a result of the Paris terrorist attacks in November 2015.

This match – originally scheduled to be held during Round 12, on 8 January 2016 – was postponed due to a European Rugby Champions Cup fixture rearrangement that occurred as a result of the Paris terrorist attacks in November 2015.

This match – originally scheduled to be held during Round 12, on 8 January 2016 – was postponed due to a European Rugby Champions Cup fixture rearrangement that occurred as a result of the Paris terrorist attacks in November 2015.