The UK research giant said that its new foothold in Poland will enable it to provide international advertisers, creative and media agencies with data from 10 central European countries.
Jean-Michel Portier, president and chief executive of TNS Media Intelligence, said: "Our strategy is to identify and work in markets that show the strongest growth in advertising and Poland is one of these countries.
"Last year, the Polish advertising expenditure grew by 13%. We carried out this policy successfully in China and Russia at the end of the 90s and have been doing the same in Europe for the past five years. It is essential for our international clients to understand these new markets and to make informed investments."
Expert Monitor was founded in 1996 by Piotr Slaby and Arkadiusz Drulis, and employs more than 50 staff.
Slaby said: "By joining TNS Media Intelligence, Expert Monitor will be able to bring new added value services and a global perspective to our clients."