Modem Media will continue to trade under its existing name, but the company expects to merge its Digitas office in London with Modem Media London, as well as in San Francisco.
Digitas said that the acquisition of Modem fitted with its growth plan. Modem's clients include AOL, Delta Airlines and General Motors, all of which are clients of Digitas.
Marc Particelli, president and CEO of Modem Media, said: "We believe that together, our clients, our employees and our shareholders benefit from the strength of our leadership.
"Our two companies have long held respect for one another and each other's people. We complement one another from a service offering standpoint and we share an enthusiasm for creating winning results for our clients."
Modem was founded in 1987 and employs 270 people in London, San Francisco and Norwalk, Connecticut. Digitas builds and runs marketing engines for clients. It is based in Boston with offices around the US and in London, and employs 1,200 people.
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