Spurs, thought to have paid £5.4million for his transfer from the Bundesliga side, did not immediately disclose the length of contract or amount paid to the German.
"For me it is amazing to be in England," said Boateng, who had also been targeted by Sevilla.
"To be in London and playing for Spurs will be great for me. It has been my ambition to play in England, I am 20 now and am about to quickly realise my dream."
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Regarded as one of the most talented youngsters in the Bundesliga last season, Boateng made 42 appearances for Hertha. He has been capped by Germany at youth and Under-21 level as well as being voted the country's best youngster last July.
"I know that Spurs are a team who like to play offensive football. The club want to climb higher next season and I want to be a part of it," he said.
"I watched the Premier League regularly in Germany, it is the most famous league in the world and I have always enjoyed it."
Having already strengthened his squad by acquiring Darren Bent, Gareth Bale, Adel Taarabt and Younes Kaboul this summer, Spurs boss Martin Jol is confident he has added another talented youngster.
"Kevin is a talented player who plays for the under-21 side of his country," Jol said.
"You could compare him with the likes of Aaron Lennon and Tom Huddlestone in that he is an exciting player for now and the future.
"He is an attacking midfield player, very strong and that is one of his main assets.
"In Germany he is regarded as one of the biggest talents, we recognised this and went in for him."
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