2009–10 LEN Euroleague
The LEN Euroleague 2009-2010 is the 47th edition of Europe's premier club water polo competition. It began on October 9 and ended on May 15.
Format
The Euroleague is run in five phases:- First qualifying round, played as a single round robin tournament at the site of one of the teams competing
- Second qualifying round, played as a single round robin tournament at the site of one of the teams competing
- Group stage, played as a double round robin, home and away
- Quarterfinals, played as a knockout round on aggregate, home and away
- Final Four, played as a single knockout tournament at a neutral site
Seeding
Seeded countriesThe eight countries with the best placed team in the preliminary rounds, or main group stage, in the previous year's competition, 2008–09 LEN Euroleague are seeded for this year's competition. Each seeded country earns 1 place in the main group stage, 1 place in the second qualifying round, and 1 place in the first qualifying round. These countries are:
| Rank | Country | Best team in the group stages of 2008–09 LEN Euroleague | Place in the group stages of 2008–09 LEN Euroleague |
| 1. | Greece | Olympiacos | Group C winner, 16 points |
| 1. | Serbia | VK Partizan | Group D winner, 16 points |
| 3. | Italy | Pro Recco | Group A winner, 12 points |
| 4. | Montenegro | PVK Jadran | Group B winner, 11 points |
| 5. | Hungary | Vasas SC | Second place Group D, 12 points |
| 6. | Croatia | HAVK Mladost | Second place Group B, 10 points |
| 7. | Russia | Spartak Volgograd | Third place Group A, 9 points |
| 8. | Spain | CN Atlètic Barceloneta | Fourth place Group B, 5 points |
| 9. | France | Cercle des Nageurs de Marseille | Fourth place Group D, 2 points |
Unseeded countries
All other countries were invited to enter up to two clubs into the first qualifying round.
Entries
| First Qualifying Round | How qualified |
 Amateur Schwimm Club Duisburg e.V. | Playoff finalist, German Bundesliga 2008/09 |
 AŠD Vaterpolo Koper Rokava | Slovenian Champions 2008/09 |
 Brixia Leonessa Nuoto SSD A R.L. | 3rd place playoff winner, Serie A1 2008/09 |
 Cercle des Nageurs de Marseille | Winner, final four playoff, Championnat de France Elite 2008/09 |
 ČH Hornets Košice | Slovakian Champions 2008/09 |
 CSM Frigoconti Oradea | Romanian Super League Champions 2008/09 |
 Galatasaray Men's Water Polo Team | Turkish Premier League Champions 2008/09 |
 LSTW Lodz | Winner Polish Championship 2009 |
| Olympic Nice Natation | Runner-up, final four playoff, Championnat de France Elite 2008/09 |
 Portinado | Portuguese Cup Champions 2009 |
 PVK Rabotnicki - Skopje | Macedonian Champions 2008/09 |
 Sintez Kazan | 3rd place, Russian League 2008/09 |
 T-Mobile Honvéd | 3rd place playoff winner, Hungarian Championship 2008/09 |
 Vaterpolo Club Niš | 3rd place playoff winner Serbian Championship 2008/09 |
 Vaterpolo Klub Šibenik | 3rd place playoff winner Croatian First Division 2008/09 |
 Vouliagmeni Nautical Club | 3rd place, Greek Division A1 2008/09 |
 Wasserball Club Tirol | Austrian Bundesliga Champions 2009 |
| Wasserfreunde Spandau | Playoff winners, German Bundesliga 2008/09 |
| Second Qualifying Round | How Qualified |
| A.S.D. Circolo Nautico Posillipo | Playoff finalist, Serie A1 2008/09 |
| Havk Mladost | Playoff finalist Croatian First Division 2008/09 |
| Panionios G.S.S. Athens | Runner-up, Greek Division A1 2008/09 |
| Spartak City Volgograd | Runner-up, Russian League 2008/09 |
 Vaterpolo Klub Budva - M:TEL | Playoff finalist, Montenegren League 2009 |
| VK Primorac Kotor | 3rd place playoff winners, Montenegren League 2009 |
| VK Vojvodina Novi Sad | Playoff finalist Serbian Championship 2008/09 |
| ZF Eger | Playoff finalist, Hungarian Championship 2008/09 |
| Group Stage | How qualified |
| A.S.D. Pro Recco | Playoff winners, Serie A1 2008/09 |
| Aquatic Sport Club Shturm 2002 | Champions, Russian League 2008/09 |
 Club Natació Atlètic Barceloneta | Playoff winners, Spanish Premier Division 2008/09 |
| Jug Croatia Osiguranje | Playoff winners Croatian First Division 2008/09 |
| Olympiacos | Champions, Greek Division A1 2008/09 |
| SWC Jadran CBK - Herceg Novi | Playoff winners, Montenegren League 2009 |
| Teva - Vasasplaket Budapest | Playoff winners, Hungarian Championship 2008/09 |
| WPC Partizan Raiffeisen | Playoff winners Serbian Championship 2008/09 |
First qualifying round
| Key to colors in group tables |
| Progress to the 2nd Qualifying Round |
| Progress to the LEN Cup 2nd Qualifying Round |
Group A ([Šibenik])
Group B ([Marseille])
Group C ([Berlin])
Group D ([Košice])
Second qualifying round
Group E ([Eger])
Group F ([Budva])
Group G ([Naples])
Group G ([Athens])
Preliminary round
| Key to colors in group tables |
| Group winners and runners-up advanced to the [|Quarter-finals] |