"It feels good, it feels special. Many people know that I've had a special bond with this club growing up," Wilshere told West Ham's website.
"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.
"My family and a few of my friends are West Ham fans so everyone's buzzing."
Wilshere made his senior debut for Arsenal in 2008, going on to make 197 appearances and winning the FA Cup twice -- in 2014 and 2015.
A mixture of injuries and loss of form saw him struggle to secure a regular first team spot and he spent the 2016-17 season on loan at Bournemouth.
He impressed on his return to Arsenal last season but the 34-cap England international was unable to force his way into the squad for the World Cup.
Wilshere will fly to Switzerland to join new West Ham manager Manuel Pellegrini's squad at their pre-season training camp in Bad Ragaz.
West Ham finished 13th in their last campaign. They play the first game of the 2018-19 season on Aug. 12 at Liverpool.
(Reporting by Shrivathsa Sridhar in Bengaluru; Editing by Christian Radnedge)
