The "changing architecture" of European big business is significant in that it challenges traditional forms of industrial collective action in Europe. The creation of European-level big business organisations has allowed large companies to bypass long-established European as well as national industry associations in influencing EU legislation and programs. Thus, European and national industry associations--long recognised as the voice of industry--must now coordinate or compete with large companies not only for influence in EU industrial and regulatory policy, but also for membership and dues. The purpose of this paper is to examine large firms' collective action in the European Union. Why did these large companies organize themselves at the European level? How did the collective action of big business differ from that of traditional industry associations? What influence has the mobilisation of European multinationals had on these associations? Why and how are big business association strategies changing in the post-Single Market era? In addressing these questions, the paper will explore the changing architecture of European big-business organisations in the history of the European Union