Reading bring in Hoffenheim's Williams
The 24-year old German-born USA international has penned a four-year with the Royals who are preparing for the 2013/14 season in the Championship.
"I am very excited to be here, I am really looking forward to the season and to try to get the club back to the Premier League," he told the club's official website.
"I spoke to the manager Nigel Adkins when I did my medicine check and he is a really great, nice guy. I'm looking forward to working with him.
"I would like to say to the Reading fans I will give 100% every game, I am proud to wear this jersey and will do everything to help this team back to the Premier League."