Riether has joined the Cottagers from FC Cologne.
He met his new team-mates for the first time when the Fulham squad returned for pre-season training on a drizzly Monday at Motspur Park.
"I'm very happy to be here," he told fulhamfc.com. "It's always a great experience to change club and to change to a new country. In Germany they say the Premier League is the best league in the world and for me it is a great honour to be at a big Club with a big tradition like Fulham. I hope I can help Fulham progress in the right direction.
"At first, I have to get to know the players, the Club, the crowd and the fans. We want to be successful, I won't say which place we will reach in the league but we will see how we start and I hope we have a good season."
He continued: "It's a big step for me as I have always played in Germany. I learned English in school but I have to learn more.
"I have been here for a few days and it has almost always been raining! I hope the summer comes soon. But it's quite good for pre-season as it's not too hot."