Riether's departure from Fulham continues something of an exodus at the Craven Cottage club following their relegation from the Premier League.
A Fulham statement released on Thursday said: "The club can confirm that defender Sascha Riether has joined Bundesliga side SC Freiburg on a permanent basis for an undisclosed fee.
"The 31-year-old right-back moved to Fulham on a season-long loan from FC Cologne in early July 2012, with the club taking up an option to acquire the player on a permanent basis the following summer.
"Capped twice by Germany, Riether made 72 appearances for Fulham during his two seasons at the club, scoring once in a 2-2 draw at Sunderland.
"The club would like to thank Sascha for his service and wishes him the very best for the future."
Freiburg finished 14th in the Bundesliga last term.