Gera was a crowd favourite during a four-year stint at the Hawthorns before moving to Fulham on a free transfer in 2008.
"I think it's a massive coup for the club that we have been able to persuade him to come back to West Brom despite the many other offers he had, because he is a player who is widely appreciated in the Premier League and abroad," West Brom manager Roy Hodgson, who also signed Gera for Fulham, told the club's website.
Gera, 32, is currently recovering from an ankle injury that will sideline him until the middle of September.
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