If a trial is multinational, who appoints the Principal Investigator (PI) for every participating site?

The Chief Investigator (CI)

The Chief Investigator (CI), who is sometimes referred to as the Co-ordinating Investigator or Investigator depending on the geographical location (like outside the UK), serves as the lead researcher providing scientific and operational leadership flowing from the Sponsor. In the context of large, complex studies that span multiple sites, especially those conducted across different countries or regions (multinational trials), the CI is the designated individual responsible for coordinating this network. As part of their central leadership duties, the CI formally appoints a Principal Investigator (PI) to assume direct responsibility for the trial conduct at each individual participating site. While the CI may sometimes take on the role of a PI at one of the sites they oversee, their overarching responsibility includes establishing the leadership structure across all trial locations.