G2, which describes itself as an activation marketing and brand communications company, said the investment in MDS Boole was part of WPP's strategy to forge links with important market sectors.
The Madrid-based firm, which employs just 18 people, was founded in 2003 and has a client base including Nokia, Diageo, Seat and Vodafone.
The company specialises in data analytics and metric consultancy, recording revenues for the year ending December 2005 of €1.3m.
Activation marketing, according to G2, is an alternative to traditional marketing methods.
G2 claims that its activation marketing ethos can help generate greater return for businesses by using better online, point of sale and direct marketing techniques that "activate the relationship between the brand and the consumer".
The sum of G2's investment has not been disclosed.
If you have an opinion on this or any other issue raised on Brand Republic, join the debate in the .