Many corporations with large in-house advertising depart-ments also employ ad agencies to prepare and place theiradvertising. Similarly, a corporation or other organization may have its own large public relations or corporate communications department, yet supplement its own efforts by retaining outside specialists. These specialists are known as PR counsel firms or PR agencies. PR firms function very much like advertising agencies. In fact,many PRfirms are owned by advertising companies. Three global advertising leaders, the WPP Group, Omnicom, and the Interpublic Group, own 7 of the top 10 PR firms.