The Brawn BGP 001 (originally known as the Honda RA109) is a Formula One world championship winning racing car, the design of which was started by Honda Racing, and completed and then built by the team after it was renamed to Brawn GP. It was the first and only Formula One car constructed by the Brawn GP team, and was used to contest the 2009 Formula One season. The car won eight out of the seventeen Grands Prix it competed in. It was notable for its unusual double diffuser, and its legality was disputed, though it was ultimately deemed legal by the FIA. This is the first Brackley-based F1 car to utilise Mercedes-Benz engines, which is used by its successor factory team. The BGP 001 was the last Mercedes customer team to win the Constructors' Championship until the McLaren MCL38 in 2024.

The BGP 001 made its competitive debut at the 2009 Australian Grand Prix, where Jenson Button took pole position in qualifying and finished first in the race while his teammate Rubens Barrichello took second place in both qualifying and race. During the first half of the season alone, Button took seven further podiums, including six wins, which, due to a mid-season drop in performance from the team which meant he did not score any further victories, gave him enough momentum to secure his first Drivers' Championship. Barrichello took six podiums, including two wins, though he dropped to third behind Red Bull's Sebastian Vettel.

Honda Racing began development for their 2009 car early in the 2008 season. In December 2008, Honda announced their plans to withdraw from Formula One. Development of what would become the BGP 001 continued whilst a buyer was sought for the team. The team were purchased by Team Principal Ross Brawn, and the outfit renamed Brawn GP. It was designed by Loïc Bigois, in similar respects to all the other cars on the grid with a moulded carbon fibre and honeycomb composite monocoque and a front and rear wishbone and pushrod activated suspension system. Remarkably, it was revealed that the modifications made to the car to accommodate its Mercedes engine saw six inches removed from the rear end, severely compromising the car's center of gravity and by the time the team realized how much the car's balance had changed, there was no time to commission a new design. Ross Brawn also admitted that there were fundamental problems with the car, stating that it was too heavy, and that some of the parts were not good for the car.

Yet the car had one difference, which was focused on the rear so-called 'double-decker diffuser'. The diffuser is at the rear of the car and is a route to get downforce by using the airflow under the car's floor. The BGP 001 had a different central channel to its diffuser with the shape of the structure being used to create advanced type of double-decker design. The diffuser's controversial aspect was the hole in the rear which increases the speed of airflow as it heads towards the higher rear venturi section, where it expands and creates more downforce. Other teams argued that the presence of the hole was against the regulations.

At the first race of the season in Australia an official complaint was launched by Renault, Red Bull and Ferrari against the diffusers of the Williams FW31, Toyota TF109 and the BGP 001 saying that they were illegal. However the race stewards did not share that view and rejected the other teams' complaints. Subsequently, the car was cleared to race in Melbourne. The same problem was faced in Malaysia after BMW tried again but failed.

Over the controversy the 'non-diffuser' teams, Ferrari, BMW Sauber, Red Bull, lodged an official appeal against the design and the date was set for April 13, 2009 for the FIA International Court of appeal (ICA); putting the first two races under appeal meaning the cars' first two wins of the season with Button could have been removed. After discussing the legality of the diffusers throughout Tuesday a verdict was becoming clear. On Wednesday 14th the ICA concluded that the diffusers' designs were legal and complied with the 2009 regulations, rejecting the teams' appeal.

With the diffuser change, the new rules in place for the 2009 season required cars to have narrower and higher rear wings and wider and lower front wings, designed to reduce air disturbance for following cars and hence make overtaking easier. Slick tyres were also re-introduced in the 2009 Formula One season, having been absent since 1998, this said to increase tyre grip by about 20%.

The BGP 001 used a Mercedes-Benz FO 108W engine, supplied through a customer deal. Per the 2009 regulations, the engine was a naturally aspirated V8 and was rev-limited to 18,000 rpm. Originally the car was engineered for a Honda-designed engine, however, when Honda announced their withdrawal from the sport, a customer deal with Mercedes was obtained. It was reported that deals with Ferrari and Mercedes were available, the latter being chosen as it was simpler to integrate into the existing car. However, an unnamed senior Brawn GP engineer, after the title-winning race in Brazil, was reported saying that significant and unconventional changes were made to accommodate the FO108W engine. Simon Cole, Brawn's chief trackside engineer, alluded that the team had decided against using Ferrari engines for fear that Ferrari would control the car's engine performance and not let a customer team beat them.