The Hammers announced the transfer with this clip on social media:
Having left Arsenal following the expiration of his contract at the end of last season, the midfielder makes the switch to the east London club on a free transfer.
"It feels good, it feels special," Wilshere, whose dad and brother are West Ham supporters, said to the club's official website. "Many people know that I've had a special bond with this club growing up. People will have seen the picture of me in a West Ham shirt and I've got good memories of my childhood supporting West Ham, watching them at Upton Park."
Wilshere arrives at West Ham amid what has been a busy summer for the club in the transfer window so far.
New Hammers boss Manuel Pellegrini has already added Lukasz Fabianski, Issa Diop and Ryan Fredericks to his squad. According to BBC Sport, they are also close to getting a deal done for Borussia Dortmund winger Andriy Yarmolenko.
James Benge of the Evening Standard believes the Hammers have landed a fine player in the England international:
Wilshere heads to West Ham seeking to reignite a career that has stalled in recent years at the Emirates Stadium.
Despite showing immense potential as a teenager, the midfielder has failed to live up to the expectations so many had for him. In the main, that's due to injury problems, with the England international besieged by a number of issues—last term he started just 12 times in the top flight for Arsenal.
Nevertheless, there's no doubt there's talent to still tap into. He still showed flashes of brilliance for the Gunners last season and remains a player who can unlock the opposition with a defence-splitting pass or a surge forward.
Even so, as noted by the Football Ramble, there didn't appear to be many major clubs ready to take a punt on Wilshere:
The upcoming season will be a huge one for the midfielder, as he will now be handed the chance to show he is still a high-class operator in English football's top flight. Perhaps even more crucially, it will be imperative for him to string together games in succession and build up some much-needed fitness.
While Wilshere has long been associated with Arsenal, the move to West Ham will clearly be stirring for him given the ties to the club his family has. That emotional stimulation and the chance of regular football means this move provides the ideal environment for the 26-year-old to get his career back on track again.