Shield Mark, based in Amsterdam, has 23 trade mark attorneys and more than 70 staff in total. It has until now concentrated on trade mark and design work, but following the merger will also provide patent services.
The merger will give Zacco a foothold in the Benelux market. It already has seven offices in Denmark, Norway and Sweden.
In Managing IPs survey of the largest firms published in September 2007, Zacco was ranked 11th in Europe with 91 practitioners.
Zacco chief executive Hans-Bertil Håkansson said in a statement that the firm "wants to move from being a regional Scandinavian player to become a European player with global reach by being active in the restructuring of the European IP service market".
Shield Mark will retain its name for the time being and will be headed by Alice Slabbaert.