Felipe Massa has revealed that he joined Williams because the Wantage-based team offered him the chance to be the lead driver.
The Brazilian has been the number two to Fernando Alonso at Ferrari since 2010, but after he was replaced by Kimi Raikkonen for the 2014 season, the 32-year-old was eager to shake the role as number two off.
"The most important thing is that Williams wants to have me," Massa told Autosport about his motivation for choosing Williams.
"That's a really good thing, to go to a team that wants to have you to lead so I'm really happy about that.
"I've been really happy with my job in the second part of the season, so I'm really looking forward to having a very good last two races for Ferrari.
"I'm motivated and ready to do a good job with Williams."
Massa added that he believes the experience he picked up during his eight years at Ferrari, as well as the rule changes that take effect next year, will give Williams the opportunity to make big steps forward in 2014.
"I think I have a lot to give to Williams as I have a lot of experience from a long time with Ferrari," Massa continued.
"I know I can do a lot, especially with the big rule changes that we are going to have.
"I'm really happy with my choice and really ready to work as hard as I can to help Williams, also being part of a very important growing up compared to the season they have had.
"That's what I'm looking for and ready for [a long-term Williams future].
"It's not just a one-year contract, it's more than that so I am very happy and ready to work as hard as I can."