2018–19 European Rugby Champions Cup pool stage
The 2018–19 European Rugby Champions Cup pool stage is the first stage of the 24th season of European club rugby union, and the fifth 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 12-14 October 2018, and ended following 6 rounds of games, on the weekend of 18-20 January 2019.
Seeding
The twenty 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. For example, a losing quarter-finalist would be seeded below a losing semi-finalist, even if they finished above them in the regular season.
| Rank | Top 14 | Premiership | Pro14 |
| 1 |  Castres |  Saracens |  Leinster |
| 2 | Montpellier | Exeter Chiefs |  Scarlets |
| 3 | Racing 92 | Wasps |  Glasgow Warriors |
| 4 | Lyon | Newcastle Falcons | Munster |
| 5 | Toulouse | Leicester Tigers | Edinburgh |
| 6 | Toulon | Bath | Cardiff Blues |
| 7 | Gloucester | Ulster |
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 and to allocate one of the three fourth seed clubs to Tier 2. The tiers are shown below. Brackets show each team's seeding and their league.
| Tier 1 | Saracens | Leinster | Castres | Scarlets | Montpellier |
| Tier 2 | Exeter Chiefs | Wasps | Glasgow Warriors | Racing 92 | Newcastle Falcons |
| Tier 3 | Munster | Lyon | Leicester Tigers | Edinburgh | Toulouse |
| Tier 4 | Bath | Cardiff Blues | Toulon | Ulster | Gloucester |
Pool stage
The following restrictions will apply to the draw:- Each pool will consist of four clubs, one from each Tier in the draw.
- Each pool must have one from each league drawn from Tier 1, 2, or 3. No pool will have a second team from the same league until the allocation of Tier 4 takes place.
- Where two Pro14 clubs compete in the same pool, they must be from different countries.
Teams in the same pool play each other twice, at home and away, in the group stage that begins on the weekend of 12/13/14 October 2018, and continues through to 18/19/20 January 2019. 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.
In the event of a tie between two or more teams, the following tie-breakers will be used, as directed by EPCR:
- Where teams have played each other
- # The club with the greater number of competition points from only matches involving tied teams.
- # If equal, the club with the best aggregate points difference from those matches.
- # If equal, the club that scored the most tries in those matches.
- Where teams remain tied and/or have not played each other in the competition
- # The club with the best aggregate points difference from the pool stage.
- # If equal, the club that scored the most tries in the pool stage.
- # If equal, the club with the fewest players suspended in the pool stage.
- # If equal, the drawing of lots will determine a club's ranking.
| Winner of each pool, advance to quarter-finals. | |
| Three highest-scoring second-place teams advance to quarter-finals. | |
| Cannot advance to the quarter-finals. |
' denotes the team has qualified for the quarter-finals as the pool winners
' denotes team has at least qualified for the quarter-finals as one of the three highest-scoring second-place teams