Leinster and Northampton are up against French sides Montpellier and Castres in what promises to be a keenly-contested pool.
Leo Cullen's side flopped in Europe last season, losing five of their six games and shipping 17 tries, but they have made a promising start in the PRO12 and head into Europe on the back of a derby win over Munster.
Montpellier are motoring nicely in the Top 14 and sit second after eight rounds of fixtures, but it's a case of the opposite for Northampton, who have struggled for consistency as well as tries.
Leinster
Champions Cup record: P142 W92 D4 L46
Best finish: Winners (2008-09, 2010-11, 2011-12)
What's hot: Johnny Sexton has hit the ground running since returning from injury and has a talented understudy in Joey Carbery. Dan Leavy and Josh van der Flier are in terrific form and with Sean O'Brien closing in on a comeback, it further increases the competition for places in the back row.
What's not: Leinster failed played to their potential against the big teams last season, particularly in Europe where they lost five of their six pool games, scoring just five tries and conceding 17.
What's changed: Robbie Henshaw and Kiwi scrum-half Jamison Gibson-Park have moved to the Irish capital with Ben Te'o, Ian Madigan and Marty Moore heading overseas.
One to watch: Robbie Henshaw returned from injury during last weekend's derby with Munster and it is worthy keeping an eye on how his centre partnership with Garry Ringrose develops.
Montpellier
Champions Cup record: P25 W9 D2 L14
Best finish: Quarter-finals (2012-13)
What's hot: Montpellier boast a huge pack and will play conservatively and to their strengths. Jake White has targeted further European glory as he bids to sign off in style. And the fact his squad is jam-packed with foreigners means they will not struggle on the road.
What's not: Les Cistes are the lead story in the soap opera that is French rugby. White has ripped the soul out of Montpellier by signing half of South Africa. The absence of hooker Bismarck du Plessis due to injury will be sorely felt.
What's changed: Academy product Francois Trinh-Duc has departed after a public falling out with White, but Nemani Nadolo, Alexandre Dumoulin and Joe Tomane have bolstered the backline.
One to watch: Nadolo was a star in Super Rugby and has already scored a hat-trick in the Top 14. He will terrorise defences in the Champions Cup.
Northampton Saints
Champions Cup record: P97 W58 D1 L38
Best finish: Winners (1999-2000)
What's hot: Louis Picamoles has quickly settled into life in the Premiership and George North is rediscovering the form that made him the most feared winger in the northern hemisphere.
What's not: Saints have been shaky on home soil, losing two of three games at Franklin's Gardens this season and scraping past Exeter in the other. They cannot afford a repeat in Europe.
What's changed: Nic Groom has filled the void left by Kahn Fotuali'I while Campese Ma'afu - the brother of former Saint Salesi - has joined the club along with fellow Fiji forward Api Ratuniyarawa.
One to watch: France No 8 Picamoles will bring the intensity and go-forward Northampton have craved since Samu Manoa left the club last year.
Castres
Champions Cup record: P70 W25 D1 L44
Best finish: Semi-finals (2001-02)
What's hot: Castres are a ridiculously stubborn side and boast one of the tightest defences in the Top 14. Their pack, led by try-scoring No 8 Alex Tulou, will give them go-forward, half-backs Rory Kockott and Benjamín Urdapilleta bring control and wing David Smith provides stardust.
What's not: This is Castres' 13th season in the European Cup and they have reached the knockout stages on just one occasion.
What's changed: The Stade Pierre-Antoine remains a difficult place to play but Castres are also finding some form on the road. They will be targeting an upset when they visit Leinster in round one.
One to watch: Alex Tulou scored nine tries in the Top 14 last season and his powerful ball-carrying spells trouble for opposition defences.