Watford announced the dual signings of goalkeeper Ben Foster from West Brom and Sweden winger Ken Sema from Ostersunds on Thursday.
Foster, 35, signed a two-year deal with a club option for another season, ending a seven-year spell with the Baggies, who were relegated in May.
The goalkeeper reportedly refused to join West Brom on a preseason trip to Portugal.
Foster has previously played for Watford on loan between 2005 and 2006, making 81 appearances and helping them win promotion to the Premier League in 2006.
Sema, 24, signed a five-year deal after helping Ostersunds reach the Europa League knockout stage last season.
His goal against Arsenal gave Ostersunds a second-leg victory in the round of 32, but the Gunners still advanced comfortably on aggregate.
Sema has made five appearances for Sweden but was not included in the World Cup squad that will face England this weekend.
