Turkish champions have secured the services for German midfielder Michael Fink, who makes the move from Bundesliga side Eintracht Frankfurt.
The defensive midfielder played for Frankfurt since 2006 and had a particularly good 2008-09 season in which he scored five goals.
Besiktas reportedly agreed to pay 1.2 million Euros for the player, who signs a deal for the coming three years.
In Istanbul, the 27-year-old Fink teams up with fellow countryman Fabian Ernst who joined Besiktas from Schalke 04 during the January transfer windows.