The 30-year-old, who will be 31 in three months' time, returns after two seasons with the Cottagers in West London, having moved to the Premier League in 2012 following the relegation of his last Bundesliga club 1. FC Köln.
Club going places
"I had a wonderful time in London but now I'm looking forward to playing in the Bundesliga again. I'm not just coming back to Freiburg for nostalgic reasons. I've also come back because I've seen Freiburg develop extremely well in recent seasons. I want to do whatever I can to help the team, the coaching staff and the coach Christian Streich to ensure our Bundesliga status as quickly as possible next season."
Riether spent five years in the Freiburg first team before moving to VfL Wolfsburg in 2007, with whom he won the Bundesliga title in 2009. He spent one season at Köln between 2011 and 2012 before transferring to Fulham, initially on loan, playing 66 times in the Premier League and being voted the club's player of the season for 2012/13.
He is set to resume a career that has comprised 207 top-flight appearances and ten goals when the Bundesliga returns on Friday 22 August.