The 2015–16 European Rugby Champions Cup pool stage was the first stage of the 21st season of European club rugby union, and the second under the European Rugby Champions Cup format.

Twenty teams were seeded based on their performance in the three major European domestic leagues - the Premiership, the Pro12 and the Top 14.

Teams were seeded based on their performance in the regular season, and, where applicable, subsequent play-off to determine a league champion.

Where teams were eliminated in the same round of a knock-out tournament, their league position at the end of the regular season determined which team received a higher seed.

During the pool stage, the teams will play the 3 other teams in their pool twice, both at home and away,[3] Based on the result of the match, teams receive competition points as follows:[4] Following the pool stage, the five winners from each group progress to the quarter-finals, along with the three best pool runners-up from the competition (the three of the five runners-up with the highest number of competition points).