The 2008–09 Heineken Cup was the fourteenth edition of the Heineken Cup, the annual rugby union European club competition for clubs from the top six nations in European rugby.

Irish side Leinster became the champions, defeating Leicester Tigers 19–16 in the final.

[3] Other nations had their usual number of participants: England six, Ireland three, Italy two and Scotland two.

[4] The seeding system for participating teams changed from previous editions of the Heineken Cup.

[7] The brackets show each team's European Rugby Club Ranking before the start of the 2008–09 season.