Former world champions Williams are hoping to continue the progress they made last year, after unveiling their new Formula One car.
The last of the 11 teams to show off their new car, Williams hope the FW35 will be an improvement on the FW34 that took Venezuelan Pastor Maldonado to their first victory in nearly eight years last May in Barcelona.
Founder Frank Williams, whose team are the second most successful in Formula One in terms of constructors' championships (nine) but finished last year in eighth place, believes they will have a competitive car this year.
Meanwhile on the first day of testing at Barcelona, the Mercedes driver Nico Rosberg was fastest.
The first round of the Formula One season is in Melbourne next month.