He impressed on his return to Arsenal last season but the 34-cap England worldwide was unable to force his way into the squad for the World Cup.
"On the biggest stage, he has shown that he has game-changing abilities, as well as having the creativity and intelligence to make a real difference to our squad".
The Hammers announced the signing on Monday afternoon with video on their social media, showing "Wilshere" standing outside of Arsenal tube station and, rather than getting on the tube like a normal human, flagging down a cab to take him to the London Stadium.
Suns Sign Devin Booker to Max Contract Extension
Booker, 21, is one of the NBA's elite young scorers and his extension cements his status as a major piece of the Suns' franchise. He was drafted with the number 13 pick three years ago and it has proven to be a smart decision by the Arizona-based outfit.
Prince Louis's christening to take place in the Chapel Royal
It's likely that Louis will have five godparents, as does Princess Charlotte , whereas Prince George , a future king, has seven. George was also christened in the Chapel Royal, but Charlotte was baptised at the Church of St Mary Magdalene in Sandringham.