West Brom have completed the signings of Cristian Gamboa from Rosenborg and Jason Davidson from Heracles Almelo for undisclosed fees.
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Gamboa arrives at the Baggies after having his work permit application approved by a Football Association appeal panel and has signed a three-year contract.
The 24-year-old, who started all five of Costa Rica's World Cup matches this summer, will join up with his new teammates once he has received his visa and passport.
"Cristian is a player I was extremely impressed by during the World Cup," Baggies head coach Alan Irvine told the club's official website.
"We faced stiff competition from other Premier League clubs for his services but we've managed to convince Cristian that West Bromwich Albion is the best club for him to join.
"Cristian is a quick, aggressive defender with good energy levels. He gets up and down the pitch really well and we believe he will continue to improve."
Davidson, meanwhile, has penned a two-year deal, plus a further year's option in the club's favour, after passing a medical.
The left-back featured in all three of Australia's World Cup games this summer, and Irvine is thrilled to be able to welcome him to the club.
"I'm delighted we've been able to complete a deal for Jason. He had a fantastic World Cup when he performed very well against three top teams," he said.
"Jason is a good defender who has lots of energy, gets forward well and will give us competition for places at left-back with Sebastien Pocognoli."
Gamboa and Davidson are the Baggies' eighth and ninth signings this summer following the arrivals of Brown Ideye, Craig Gardner, Joleon Lescott, Chris Baird, Sebastien Pocognoli and Jason Davidson, as well as Andre Wisdom on loan.