The film focuses primarily on the interviews of former Secretary of Defense, Robert McNamara, who was interviewed for about 20 hours by the director of the documentary, Errol Morris, through a special device called the "Interrotron" which projects images of interviewer and interviewee on two-way mirrors in front of their respective cameras so each appears to be talking directly to the other. Use of this device is intended to convey actual interaction with each other and direct eye contact with the viewer.