The American forward, who finished last season on loan at Bursaspor, used the social media site to confirm his move to AZ.
"To all my amazing fans, I have indeed agreed to terms to join AZ In holland!" he wrote. "Thanks for all the love and the hate it's all making me better!"
With the striker clearly not in favor at Villarreal and in need of regular playing time, rumors of where Altidore would land have been circulating all summer. The move to AZ should give him the chance to find those regular minutes.
Altidore played a key part for the United States in the early part of the 2011 Gold Cup, scoring twice before picking up an injury in the quarterfinal against Jamaica which kept him out of the semifinal against Panama and the final against Mexico.
The move to Holland will make it the fourth country the striker has played in since leaving Major League Soccer for Europe, having already spent time in Spain, England and Turkey.