The 25-year-old joins up with his new club ahead of the Matchday 19 trip to Eintracht Frankfurt, having agreed terms on a deal that will keep him at the club until 2015.
"Plenty of Bundesliga experience"
Polanski started out at Borussia Mönchengladbach in 2004/05, before joining La Liga side FC Getafe four years later. After making 26 appearances in Spain's top-flight, Polanski returned to Germany in 2009/10 with Mainz 05, where he went on to play 87 times in the Bundesliga, scoring four goals in the process.
"Eugen Polanski has plenty of Bundesliga experience and tactically-speaking is well schooled. He brings that extra bit of stability that we undoubtedly need to avoid relegation," said Hoffenheim sporting director Andreas Müller.