The defender, who turned 22 on Friday, put pen to paper on a deal that will run until 30 June 2018.
'Calm, aggressive and positionally astute'
Kim, who joins from Japanese J-League outfit Albirex Niigata, said he was looking forward to the "challenge of playing in the Bundesliga". The left-back is already a mainstay in the South Korean national team and would ordinarily be with his compatriots at the World Cup in Brazil, but he is carrying an ankle injury that means he is not able to add to his nine international caps for the time being.
"It's a massive shame for him," said Hoffenheim sporting director Alexander Rosen, who is nevertheless delighted to have captured a "calm, aggressive and positionally-astute defender. The fact that such a young player is already a leading member of the team speaks volumes."