From Honda to Yamaha

There was much speculation during the second half of the 2003 season about Rossi's plans for the future. Some people suspected that he would succeed in his bid to claim a third consecutive title and wondered where he would go in the future. His contract with Honda was up at the end of the year and there were rumors that Rossi had become somewhat disillusioned with his ride at Honda. His tenure at Honda had effectively run its course; he had provided Honda with a 500 cc World Championship as well as consecutive MotoGP World Championships.
Partnered with increased scepticism that the reason for his success was the dominance of the RC211V rather than Rossi, it was inevitable that Honda and Rossi would part. Mid-season rumors pointed towards a possible move to Ducati, which sent the Italian press into a frenzy; the concept of the great Italian on the great Italian bike seemed too good to be true. Ducati did indeed try to seduce Rossi into riding their MotoGP bike, the Desmosedici, but for numerous reasons Rossi passed the offer up. Critics say that compared to the other manufacturers, Ducati had a significant way to go before being competitive even with Rossi at the helm. This proved to be the truth with Ducati's lacklustre performance in the 2004 season, which had actually been worse than their inaugural year in MotoGP in 2003.
In his 2005 autobiography, "What If I'd Never Tried It?", Rossi offers another reason for choosing Yamaha over Ducati, saying that the mindset at Ducati Corse was a little too similar to the one he was trying to escape from at Honda.
Ultimately, Rossi signed a two-year contract with rivals Yamaha reportedly worth in excess of (U.S) $12 million; a price no other manufacturer, even Honda, was willing to pay.