Williams have announced they are to switch to Toyota engines next season in a new three-year deal.
Nico Rosberg has picked up just four points for Williams this season
Williams, who are currently powered by Cosworth after their split with BMW, will use the same specification engines as Toyota's own team.
"The agreement is the cornerstone of a challenge for the world championship," said team boss Frank Williams.
"We are proud to have secured their support in our efforts to return to our competitive best."
Williams have won 113 Grands Prix since 1979 and nine constructors' championships.
But their last titles were in 1997, when Canadian Jacques Villeneuve also won the drivers' crown.
They are currently eighth in this season's constructors' standings with 10 points while Toyota are fifth with 21.
Toyota entered F1 in 2002 but have yet to win a Grand Prix despite having one of the biggest budgets in the sport.
The new deal with Williams will mean the end of their agreement with the Midland team.
While Williams remain an independent team, the engine agreement could lead to greater cooperation with Toyota in future.
Williams said: "Toyota is an impressive and remarkable industrial giant, with the most phenomenal reputation for achieving the goals it sets itself.
"Both Williams and Toyota Racing see significant benefits from a relationship based on robust on-track competition and close off-track co-operation."
Toyota motorsport president John Howett added: "We are pleased to be selected as the engine provider to Williams and look forward to establish a strong relationship with them.
"We look forward to both teams using each other as a comparative benchmark from which each can improve its own performance and to competing with each other at the front of the grid."