The 2017–18 European Rugby Champions Cup pool stage is the first stage of the 23rd season of European club rugby union, and the fourth under the European Rugby Champions Cup format.
The competition involves twenty teams, across five pools of four teams, for eight quarter-final places – awarded to the five pool winners and the three top-ranked pool runners-up.
The pool stage began on the weekend of 13–15 October 2017, and ended following round 6, on the weekend of 19–21 January 2018.
The 20 competing teams are seeded and split into four tiers, each containing five teams.
For the purpose of creating the tiers, clubs are ranked based on their domestic league performances and on their qualification for the knockout phases of their championships, so a losing quarter-finalist in the Top 14 would be seeded below a losing semi-finalist, even if they finished above them in the regular season.[1]
| width=5% | Rank | width=19% | Top 14 | width=19% | Premiership | width=19% | Pro 12 |
|---|---|---|---|---|---|---|---|
| 1 | Scarlets | ||||||
| 2 | Munster | ||||||
| 3 | Leinster | ||||||
| 4 | Ospreys | ||||||
| 5 | Ulster | ||||||
| 6 | Glasgow Warriors | ||||||
| 7 |  Benetton |
Based on these seedings, teams are placed into one of the four tiers, with the top seed clubs being put in Tier 1. The nature of the tier system means that a draw is needed to allocate two of the three second seed clubs to Tier 1. The tiers are shown below. Brackets show each team's seeding and their league (for example, 1 Top 14 indicates the team was seeded 1st from the Top 14).
| width=5% | Tier 1 | width=19% | Exeter Chiefs (1 AP) | width=19% | Scarlets (1 Pro12) | width=19% |  Clermont (1 Top 14) | width=19% | Wasps (2 AP) | width=19% | Munster (2 Pro12) | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| width=5% | Tier 2 | width=19% | Toulon (2 Top 14) | width=19% | Saracens (3 AP) | width=19% | Leinster (3 Pro12) | width=19% | La Rochelle (3 Top 14) | width=19% | Racing 92 (4 Top 14) | |
| width=5% | Tier 3 | width=19% | Leicester Tigers (4 AP) | width=19% | Ospreys (4 Pro12) | width=19% | Bath Rugby (5 AP) | width=19% | Ulster (5 Pro12) | width=19% | Montpellier (5 Top 14) | |
| width=5% | Tier 4 | width=19% | Harlequins (6 AP) | width=19% | Glasgow Warriors (6 Pro12) | width=19% | Castres (6 Top 14) | width=19% | Benetton (7 Pro12) | width=19% | Northampton Saints (Play-off) |
The following restrictions will apply to the draw:
The draw took place on 8 June 2017, in Neuchâtel, Switzerland.[2]
Teams in the same pool play each other twice, at home and away, in the group stage that begins on the weekend of 13/14/15 October 2017, and continues through to 19/20/21 January 2018. The five pool winners and three best runners-up progress to the quarter-finals.
Teams are awarded group points based on match performances. Four points are awarded for a win, two points for a draw, one attacking bonus point for scoring four or more tries in a match and one defensive bonus point for losing a match by seven points or fewer.[3]
In the event of a tie between two or more teams, the following tie-breakers will be used, as directed by EPCR:
| Winner of each pool, advance to quarter-finals. | ||
| Three highest-scoring second-place teams advance to quarter-finals. | ||
| Cannot advance to the quarter-finals. |
(Q) denotes the team has qualified for the quarter-finals as the pool winners
(q) denotes team has at least qualified for the quarter-finals as one of the three highest-scoring second-place teams
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