Eriksen, a crafty playmaker who has been capped 37 times for his country, becomes the latest attacking addition to the north London club's burgeoning ranks.
The 21-year-old will be Tottenham's seventh transfer window acquisition and with media reports putting the fee in the region of 12 million pounds ($18.6 million), the move is likely to take the club's spending to over 100 million.
"We are delighted to announce that we have reached agreement with Ajax for the transfer of Christian Eriksen," Spurs said on their website (www.tottenhamhotspur.com) above a photo of the player holding a Tottenham shirt.
Eriksen joined Ajax in 2008 from Denmark's OB Odense and played 161 games for the club, scoring 33 goals.
He won three Dutch championships between 2011 and 2013 and was named Dutch Football Talent of the Year and Ajax Talent of the Year in 2011.
Paulinho, Nacer Chadli, Roberto Soldado, Etienne Capoue, Erik Lamela and Vlad Chiriches have joined Tottenham in the transfer window, but the huge outlay is likely to be offset by Gareth Bale's anticipated world-record move to Real Madrid.
($1 = 0.6465 British pounds)
(Reporting by Toby Davis; editing by Ed Osmond)