Alonso was due to be a free agent for 2009 had Renault finished lower than third in the constructors' championship.
Honda made signing Alonso to a £7.6 million contract its main priority; he reportedly considered the offer due to the arrival of Ross Brawn as its team principal.
Late in 2008, Christian Horner, the Red Bull team principal, and the adviser Helmut Marko presented Flavio Bratore with a two-year contract for Alonso covering 2009 and 2010.
Alonso declined the offer because he would only commit to Red Bull for one season, and signed a two-year contract with Renault on 5 November.
He expressed his and Renault's aim to win the championship and was aware it would be difficult to achieve: "When you win a drivers' title, winning the constructors' one is more special because usually it's harder to score points.
So winning both titles is our goal.
That was very hard to do last year, but then, when we were strong in the final races our goals changed."

The R29 proved to be more noncompetitive than its predecessor due to the car lacking a dual diffuser system and pace.
Alonso eschewed an aerodynamic front wing mandated in an attempt to make overtaking more possible since he did not believe it would benefit him.
He scored points in eight races and took one podium result: a third-place finish at the season's 14th round, the Singapore Grand Prix.
Alonso won for the Hungarian Grand Prix and led the first 12 laps before he retired due to an incorrectly fitted right-front wheel.
Alonso was ninth in the drivers' championship with 26 points, his lowest placing since he came sixth in the 2003 season; he maintained his reputation as one of Formula One's best drivers.
Alonso was due to be a free agent for 2009 had Renault finished lower than third in the constructors' championship. Honda made signing Alonso to a £7.6 million contract its main priority; he reportedly considered the offer due to the arrival of Ross Brawn as its team principal. Late in 2008, Christian Horner, the Red Bull team principal, and the adviser Helmut Marko presented Flavio Bratore with a two-year contract for Alonso covering 2009 and 2010. Alonso declined the offer because he would only commit to Red Bull for one season, and signed a two-year contract with Renault on 5 November. He expressed his and Renault's aim to win the championship and was aware it would be difficult to achieve: "When you win a drivers' title, winning the constructors' one is more special because usually it's harder to score points. So winning both titles is our goal. That was very hard to do last year, but then, when we were strong in the final races our goals changed."
The R29 proved to be more noncompetitive than its predecessor due to the car lacking a dual diffuser system and pace. Alonso eschewed an aerodynamic front wing mandated in an attempt to make overtaking more possible since he did not believe it would benefit him. He scored points in eight races and took one podium result: a third-place finish at the season's 14th round, the Singapore Grand Prix. Alonso won for the Hungarian Grand Prix and led the first 12 laps before he retired due to an incorrectly fitted right-front wheel. Alonso was ninth in the drivers' championship with 26 points, his lowest placing since he came sixth in the 2003 season; he maintained his reputation as one of Formula One's best drivers.
Motor racing career of Fernando Alonso