The Werkself were in the market for a new attacking midfielder due to the departure of Toni Kroos back to Bayern Munich and head coach Jupp Heynckes considers Sam to be the perfect replacement.
"Sidney Sam has been one of the most exciting players around in the 2. Bundesliga last season and played a major role in Kaiserslautern's promotion. I think he will do a great job with us," said Heynckes on the official Bayer website.
Sam has signed a five-year deal at his new club and is Bayer's third signing of the summer transfer window.
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