| 2009 ATP World Tour Finals | |
|---|---|
| Date | 22–29 November |
| Edition | 40th (singles) / 35th (doubles) |
| Category | World Tour Finals |
| Draw | 8S / 8D |
| Prize money | $5,000,000 |
| Surface | Hard / indoor |
| Location | London, UK |
| Venue | O2 arena |
| Champions | |
| Singles | |
 Nikolay Davydenko | |
| Doubles | |
 Bob Bryan / Mike Bryan | |
The 2009 ATP World Tour Finals (also known as the 2009 Barclays ATP World Tour Finals for sponsorship reasons) was held in London, United Kingdom between 22 November and 29 November 2009. It was the first time the O2 arena hosted the ATP World Tour Year-End Singles and Doubles Championships. The event was renamed from Tennis Masters Cup to ATP World Tour Finals following the rearrangement of the ATP Tour.