Among Wilshere's first objectives at his new club will be to play his way back into the England squad, having missed out on the 23-man panel for the World Cup in Russian Federation this summer.
Speaking after signing for West Ham, the 26-year-old said he feels good joining his childhood club.
"It feels good, it feels special", Wilshere told West Ham's website.
However, Wilshere admitted on Monday that he supported the Hammers as a boy and talked about the "special bond" that he had with the club while he was growing up.
"I think I must have been about six or seven, my whole family were West Ham fans, I was a West Ham fan, still have a soft spot for them of course".
The 26-year-old joined the Gunners as a youngster in 2001, and seven years later, he got his chance to play with the big boys, and since then, he has made 197 first-team appearances.
West Ham had hoped to sign Anderson for around £35 million but have had to increase their offer.
After returning from a broken foot, Wilshere proved his fitness for Arsenal last season, making 29 starts in all competitions.
'The West Ham fans are some of the very best and I am looking forward to giving everything I have to helping the team to bring success to you all.